fe^iVOP •■•v.' ■'.V;' .^.4-;, V \ ■A'---. "• - f 'l#,-. V #v\*- -i 7 • 'fc 'A ■■.» ... ■ •■.••*• -•*■:•. •.'»""• ■.. • !-* !.\Vf'.»'i I-Ci! ^1 ■ "v ■7^7*.--r-.--Al ■ i-r ■- . ■ 'V V. ■' '-*-V= *fiT - /■ • HISTOLOGY AND HISTOCHEMISTRY OE MAN 704 Fh 1875 f in THE HISTOLOGY HISTOCHEMISTRY OF MAN. A TREATISE ON THE ELEMENTS OF COMPOSITION AND STRUCTUKE OF < THE HUMAN BODY. ^x^--1,-^. BY \ LIBRARY J HEINRICH FRE*,^ r>.°>7 PR0FB8S0K OF MEDICINB IN ZURICH. -■-_ TRANSLATED FROM THE FOURTH GERMAN EDITION, By ARTHUR E. J. BARKER, BURGEON TO THE CITY OF DUBLIN HOSPITAL; DEMONSTRATOR OF ANATOMY, ROYAL COLLEGE OF BURGEONS, IRELAND; VI8ITTN& SURGEON, CONVALESCENT HOME, 8TILLORGAN; AND REVISED BY THE AUTHOR. WITII SIX HUNDRED AND EIGHT ENGRA VINGS ON WOOD. NEW YORK: D. APPLETON AND COMPANY. 549 AND 551 BROADWAY. 1875. \&5 PREFACE. If only in the eyes of those valued friends whose kindly interest in my work has ofttimes been as great a stimulus to sustained exertion in the laborious task of translation as it has been a solace in the usual and varied delays and disappointments of publishing, I feel that perhaps some justification of myself is necessary for the late appearance of this volume ; so much later than either they or I had anticipated. The delay has in a great measure been due to my being obliged to recast a large portion of my first manuscript, in order to bring it down to a new and much enlarged and altered Fourth Edition of the original; commenced just as I had concluded my translation more than a year ago, and the "Proofs" of which I received as they Avere pressed off, and revised by the Author. The task accomplished, hoAvever, I noAv feel my regret at the delay lightened to a great extent by the consideration, that through it the value of the work is considerably enhanced, and that the latter hoav contains the most recently gathered matter from many important fields of investigation; passing, as it does, through the printer's hands, at the same time, with the last edition of the original. As regards the work which I noAv present to my medical brethren in an English dress, and which has already been translated into French, any lengthy personal testimony to its value is unnecessary. The fact that it now appears for the fourth time in a new edition is a sufficient proof of the favour AA'ith which it is regarded as a hand- book in Germany, Avhere it was recommended to myself, Avhen a student in that country, as the best work of its kind, by one of the fathers of Histology, my late valued and lamented teacher and friend, Professor Max Schultze. But I am aware this translation vi PREFACE. leaves much to be desired; and yet to those critics thoroughly familiar with German literature, I feel but little apprehension in submitting it, confident that fully conversant with the varied diffi- culties of rendering German into English, they will be lenient to its faults and careful of censure. In undertaking the work I have been actuated by the desire to render accessible to my fellow- students, young and old, a good standard work, which has been a great aid to myself in dealing with a subject as yet but little studied in English-speaking countries, and especially in my own, ;md upon which Ave possess but few native manuals. I have been prompted, moreover, by the feeling that we all need to enter more fully into the spirit of other men's researches before we can deal fairly with their theories, or deduce any practical conclusions from their investigations. And I cannot but think that a greater effort should be made by all medical men who love progress, to vindi- cate the dignity of Pathological Histology as a science in this country, and to raise it above the complacent smiles of a large class appropriating to themselves the title of " the thoroughly practical," who, for the most part, ignorant of its most elementary principles, appear to regard it as merely the pet hobby of a few vague theorisers and entirely unprofitable. General profit will only accrue to the practical surgeon or physician when, after patient toil, all are able to view the subject closely and from its many aspects. If my humble efforts to render this easier, by giving the English reader access to a compendium of the views of the greatest histologists arranged in a system, conduce, in however small a degree, to this desirable end, I shall deem my labour well bestowed. In conclusion, I have to express my cordial thanks to Professor Emerson Reynolds for some valuable suggestions in regard to chemical terms in the first part of this Avork, the " Proofs " of which he was kind enough to read over. A. E. J. B. 2 Hume Street, Dublin, October 1874. CONTENTS. Pags Introduction, §§ 1-6,..........1 L THE ELEMENTS OF COMPOSITION AND OF STRUCTURE OF THE BODY, §§ 7-64,...... n_G4 1. ELEMENTS OF COMPOSITION........11 A.. Albuminous or Protein Compounds, §§ 8-14, . . .12 Albumen, § 10,.........14 Fibrin, Fibrinogen, and Fibrinoplastin, § 11, . . . . 15 Myosin, Muscle-Fibrin, or Syntonin, § 12, . . .16 Casein,...........17 Globulin, Crystallin,........17 Peptones,..........17 Ferments,..........18 B. Hsemoglobulin. Hsemoglobulin, Haematoglobulin, Haematocrystallin, § 13, . 18 C. Histogenic Derivatives of the Albuminous Substances or Albuminoids,........21 Keratin, Mucin, Colloid, § 14.......21 Substances yielding Glutin, § 15, . . . . . .21 Collagen and Glutin,........22 Chondrigen and Chondrin,.......22 Elastic Material, Elastin,.......23 D. The Fatty Acids and Fats, § 16,.....23 Glycerin,..........23 Formic Acid, . . .......24 Acetic Acid,..........24 Butyric Acid,.........24 Capronic, Caprylic, Caprinic Acids, . .... 25 Palmitic Acid, Tripalmatin,......25 Stearic Acid, Tristearin,.......25 Oleic (Elaidic) Acid, Triolein,......25 Cerebral Matters, Cerebrin, and Lecithin, § 20, . . . 28 Cbolestearin, § 21,........30 E. The Carbohydrates, § 22,.......30 Glycogen, . ...... . . .31 Dextrin,..........32 Grape Sugar,.........32 Inosite or Muscle Sugar,.......33 Sugar of Milk, ......... 33 Vlll CONTENTS. F. Non-Nitrogenous Acids, § 23, Lactic Acid, Paralactic Acid, Oxalic Acid, Oxalate of Calcium, Succinic Acid, Carbolic Acid or Phenol, Taurylic Acid or Taurol, G. Nitrogenous Acids, § 25, . Inosinic and Hydrotinic Acids, Uric Acid, Acid Urate of Sodium and of Ammonium, Hippuric Acid, § 26, Glycocholic Acid, Glycocholate of Sodium, § 27, Taurocholic Acid, Taurocholate of Sodium, . H. Amides, Amido Acids, and Organic Bases, Urea or Carbamide, . Guanin, Hypoxanthin (Sarkin) Xanthin, § 29, Allantoin, Kreatin, Kreatinin, § 30, Leucin, § 31, Tyrosin, § 32, Glycin, § 33, Cholin (Neurin), . Taurin, § 34, Cystin, I. Animal Colouring Matters, § 35, Haematin, ..... Hydrochlorate of Haematin, Haemin, Haematoidin, .... Uroerethrin or Urobaematin, § 36, Black Pigment or Melanin, . Biliary Pigments, Bilirubin, Biliverdin, Bilifucsin, Biliprasin, K. Cyanogen Compounds, § 38,...... Sulpho-cyanogen (Rhodan), Sulphocyanide of Potassium, Page 34 34 35 35 36 36 36 36 37 38 39 40 40 40 43 43 44 45 47 48 48 48 50 50 50 50 51 52 52 53 54 54 Mineral Constituents, § 39,.......55 Oxygen,......... .56 Nitrogen,..........56 Carbonic Acid or Carbonic Dioxide,.....56 Water, § 40...........56 Hydrochloric Acid,........57 Silicic Acid,..........57 Calcium Compounds, § 41—Phosphate, Carbonate, Chloride, and Fluoride,........ . 58 Magnesium Compounds—Phosphate, Carbonate, Chloride, . 58 Sodium Compounds, § 43—Chloride, Carbonate, Phosphate, . 59 Sulphate,.....• • . . 61 Potash Compounds, § 44—Chloride, Carbonate, Phosphate, . 61 Sulphate,.........g2 Salts of Ammonium, Chloride, Carbonate, . . . .62 Iron and its Salts, Protochloride, Phosphate, . . . .02 Manganese, .......... Q2 Copper............62 CONTENTS. IX Page 2. ELEMENTS OF STRUCTURE,.......63 A. The Cell, §§ 45-58,........ 95 B. The Origin ofthe Remaining Elements of Tissue, §§59-64, 95 II. THE TISSUES OF THE BODY........103 A. Tissues composed of Simple Cells with Fluid Inter- mediate Substance, §§ 65-85,......105 1. The Blood..........105 2. The Lymph and Chyle, § 82.......131 B. Tissues composed of Simple Cells, with a small amount of Solid Intermediate Substance, §§ 86-100, . . .137 3. Epithelium, § 86,........137 4. Nail, § 99,.........160 C. Tissues belonging to the Connective Substance Group, §§ 101-155,..........164 5. Cartilage, § 103,........166 6, 7. Gelatinous and Reticular Connective Substance, §§ 113- 119,..........187 8. Fatty Tissue, §§ 120-124,......198 9. Connective Tissue, §§ 125-139,.....205 10. Tissue of Bone, §§ 140-149,......238 11. Dentiue, §§ 150-155,.......260 D. Tissues composed of Transformed, and as a rule Coher- ing Cells, with homogeneous, scanty, and more or less Solid Intermediate Substance, §§ 156-173, . . 273 12. Enamel Tissue, §§ 156-158,......273 13. Lens Tissue, §§ 159-161,......276 14. Muscle Tissue, §§ 162-173,......280 E. Composite Tissues, §§ 174-218,......305 15. Nerve Tissue, §§ 174-192,......305 16. Glandular Tissue, §§ 192-200......344 17. The Vessels, §§201-211.......362 18. The Hair, §§ 212-218........388 19. Combination of the Tissues, § 219,.....298 III. THE ORGANS OF THE BODY,.......401 A. Organs of the Vegetative Type, §§ 220-287, . .403 1. Circulatory Apparatus, §§ 220-238, . . . .403 2. Respiratory Apparatus, §§ 239-243,.....448 3. The Digestive Apparatus, §§ 244-268, . . . .458 4. The Urinary Apparatus, §§ 269-276, . . . .514 5. The Generative Apparatus, §§ 277-287, . . . .536 B. Organs of the Animal Group,......570 6. Bony Apparatus, §§ 288-289,......570 7. Muscular Apparatus, § 290,......573 8. Nervous Apparatus, §§ 291-300......574 9. Sensory Apparatus, §§ 301-326,.....603 Index...........665 MANUAL OF THE HISTOLOGY AND HISTOCHEMISTRY OF MAN. INTRODUCTION §1. Through the industry and perseverance of many talented investigators, human anatomy, as a science, had already reached an advanced stage of development so early as the close of the last century. As far as the dissecting knife could open up the structure of parts, these had been investigated in a manner sufficiently detailed for the requirements of the practical physician. And let us here offer the easy tribute of remem- brance to the name of Slimmer ring, which will ever be connected with this particular branch of study. That progress in development to be observed in all branches of natural science as a consequence of one of the nobler characteristics of human intellect, had also become manifest in anatomy. Out of a multitude of isolated facts general principles had been established. Anatomists had begun to recognise the significance of the occurrence over and over again, in the most dissimilar parts of the body, of certain definite structures, such as bone, cartilage, muscle, and nerves, but slightly or not at all modified in each, though taking a most important part in their formation. Here then, Ave have the origin of " general anatomy," the study of the structure of the body. But again, bones, cartilages, muscles, and nerves were observed each to be made up of smaller parte, and it became necessary to resolve them into those ultimate elements of form of which they are composed, in such a manner as to be able to recognise the latter in various situations. Thus the conception of an " animal tissue" originated, and Avith it the consideration of tissues, or " Histology," as a special branch of anatomical study. This, although the most important part, constitutes by no means the whole of general anatomy. By tissues we understand organic masses, in so far as they are made up of more minute parts, and receive from these their physical, chemical, anatomical, and physiological characters. The various arrangement and nature of these minute parts gives rise to the difference in what is termed the "texture" of the mass; they themselves are known as " tissue elements." But these constituents of form, these particles composing the tissues, are, in the marvellous con- 2 MANUAL OF HISTOLOGY. struction of the animal body, of such minuteness that the usual instru ments of anatomical dissection arc insufficient for their discovery and recognition, and we are therefore obliged to look around us lor otner assistance. On the other hand, a tissue, as such, may be investigated to a certain extent with the means at the disposal of an earlier epocn, Avhen there is no question as to its further resolution or insight into its ultimate composition. Indeed, we see the rudiments of histology in the first discoveries of a period long gone by. But as these coula only be of historic interest when we consider the vast strides that science na* since made, Ave shall pass them over without further comment. Fortunately for us, the science of general anatomy at the close pi the eighteenth century numbered amongst its students a highly gifted man, through whose genius it underwent an amount of development greatly to be Avondered at, when Ave consider the scanty aids to investigation ol that period. This man was M. F. X. Bichat, who died at Paris in the year IbUJ, at the early age of thirty-one, thus terminating a career memorable in the annals of medicine. Child of a stirring time, urged on by the great and celebrated philosophers of his day, and, Ave might add, inspired by that spirit of accurate investigation of Avhich science of the present day is so proud, he founded a system of histology by the help of the anatomical knife, chemical analysis, and of pathological and physiological research, Avhich his immediate successors were unable to improve upon to any considerable extent for lack of newer methods of examination. With Bichat there commenced and reached its zenith an epoch in histological research Avhich may be designated as that of investigation without the microscope—as that in Avhich the tissue-elements still remained veiled in obscurity. Remarks.—Bichat's essays are to be found in a large Avork entitled Anatomic ginirale applique d la physiologie ct a la medicine, which appeared in Paris in the year 1801, and was frequently reproduced afterwards. §2. The second epoch of histology may be termed that of microscopical research; as that of penetration dovm to the elements of the tissues. From this period our science took the name of Microscopical Anatomy, henvever inappropriate this term may be. Its first crude beginnings are lost in the clouds of a period far remote, in that age of reformative activity to which Ave owe the vigour of our modern intellectuality. In its scientific development it is the offspring of a maturer age, and the founders of the science of modern histology are many of them still alive. QThree nationalities contend for the honor of having'been the first to discover the microscope—this instrument which has enabled us to pene- trate into the regions of "The Minute." These are the English, Dutch, and Italians. There can be but little doubt, however, that the first instrument of the Find Avas constructed by a Dutch optician of the name of Z. Janssen, about the year 1590; and that Drebbel, Galilei, and Fontaaa, are incorrectly stated to be the discoverers. This much, hoAv- ever, is incontestably proved, that many microscopes had been manu- factured before the middle of the seventeenth century, and soon after came into use in scientific research. Marcello Malpighi (1628-1694), and Anton van Leeuicenhoek (1632- INTRODUCTION. 3 1723), are generally looked upon as the fathers of microscopical anatomy. The first of these made observations on the circulation of the blood, on the glands and lungs; the second, endoAved Avith indefatigable industry, saw for the first time many of the constituents of the organs of the body, Avith tolerable distinctness too, although aided by very imperfect instru- ments. But the additions Avhich Leeuwenhoek made to science, in keeping with the curiosity-loving spirit of the time, partook less of the nature of discoveries according to a definite principle, than of mere detection of strange and wonderful things, Avhere the unaided eye had previously seen nothing. The infancy of microscopical anatomy is in fact represented in him. Indeed, the exertions of the Dutch seem just devoid of that Avhich so characterised the investigations of the Frenchman Bichat, namely, that effort to combine units to a scientific whole. If we now associate with these two names those also of Swammerdam (1637-1685), and Ruysch (J.638-1734), as the discoverers and developers of our present mode of injection, Ave shall have reached the close of the first epoch of histological study defined by the discovery of the microscope. The instruments of that day Avere, hoAvever, most imperfect, so that Leeuwenhoek used simple lenses only. Hence, it is not surprising that in the hands of his successors, these microscopes, so difficult to manipulate, and so liable to deceive, became a frequent source of error. This explains the fact that Bichat preferred laying the foundations of his general anatomy Avithout their aid. After this there followed a long period of inactivity in histological research, reaching far into the nineteenth century, Avhen the science received fresh impetus from the brilliant discoveries of our own schools. Remarks.—Marcello Malpighii. Opera omnia. Lond- 1686 ; and Opera posthuma. Lond. 1697-...2. The works of Leeuwenhoek may be found in the Philosoph. Transact., and in his Opera omnia. Lugd. Bat. 1722. Arcana natural detccta. Delph. 1695. Conlinuatio arcanormn naturae detectorum. Lvgd. Bat. 1722, &c. §3. (A new era in histological research was now ushered in by the discovery of achromatism in the middle of the last century, and by the construction of achromatic object-glasses for the microscope. The first of these are said to have been made by a Dutchman named can Deyl, and a German optician of the name of Fraunhofer, in the years 1807 and 1811. Thus the microscope Avas transformed from the clumsy and deceptive imple- ment of the last century.into the elegant and accurate instrument of the present day. And now, in all the enthusiasm of novelty, the improved microscope became the means of adding discovery to discovery in the hands of many excellent German observers, so that an insight into the essential nature of the tissue-elements, and of their combination to form the various tissues, was gained in an inconceivably short time. It may suffice here, in speaking of the founding of modern histology, to mention the names of Ehrenberg, Miiller, Parkinje, R. Wagner, Valentin, and Henle. Be- sides these, many others might be added, of younger observers, who have since distinguished themselves as developers and furtherers of the science. Histology without the microscope had had a Bichat among its students; but the newer science was fortunate enough at its very outset to undergo, at the hands of Th. Schicann, the most searching and energetic elabora- 4 MANUAL OF HISTOLOGY. tion. By him the cell was proved to be the starting-point of all animal structures. He also indicated the mode of origin of the various tissues from the cell. It may be said that many points in relation to this fact were known before Schwann's time, and that he came to false conclusions in many things : but though this be true, the merit, nevertheless, remains with him of having been the first to make prominent this fundamental principle—the greatest discovery of histology—by an ovenvhelming mul- titude of facts in detail. Schwann may therefore be hailed as the founder of the science of " histogenesis," or the study of the origin of tissues—one of the most important subjects Avhich can come under our consideration, and one Avhich has more recently undergone very extensive elaboration at the hands of Rcichcrt, Koelliker, Remak, and others. Another branch of histology, again, has gradually become distinct from the study of the nature of the textures in the normal state. This, Avhich deeply affects pathology, is the consideration of the modifications Avhich tissues undergo in diseased conditions. J. Miiller may be looked upon as the originator of this particular line of study, knoAvn as "patho- logical histology," while more recently Virchoio has become famous for his great efforts in the same direction. fTo these two may be added the well-known names of some of the disciples of the latter, as, for in- stance, those of Recklinghausen, Rindfleisch, and Cohnheim. Like pathological, so is also "comparative histology " indispensable for a scientific knowledge of the finer structure of the animal frame; and yet, in spite of numerous individual efforts, and the most ingenious researches, this branch is still in its infancy, OAving to the immense amount of matter to be dealt with. To this particular field of investigation Miiller, Siebolcl, Koelliker, Leydig, and others, have devoted their great talents Avith the happiest results. Remarks.—The microscope, its construction, way to work with it, &c, has become lately the theme of many literary effusions. We will only mention here one of the more important essays on the subject—C. Robin, Du Microscope et des injections, 2d >'d., Paris, 1871. Queckett, "A Practical Treatise on the Use of the Microscope," Lond., 1848. W. Carpenter, "The Microscope," 3d ed., London, 1862. If Schacht, "Das Mikroscop," 3 Auf., Berlin, 1862. L. Beale, "How to work with the Microscope," 4th ed. ; and "The Microscope in Medicine," just published. //. Frey, " Das Mikroskop and die mikroskopische Technik," American Transl.- -(2 ) Schicann's works are to be found in an attractive little book, "Mikroskopische Untcrsuchungen liber die Ueberemstimmung in der Struktur und dem Wachstum derThiere uud Pflanzen," Berlin, 1839.—(3.) As to the rich literature of HistoW which is in its origin chiefly German (as this whole branch of anatomy is essenti'fliv the production of German industry), we shall only mention a few handbooks and other similar aids, and even these only sparingly. Among the older works which deserve mention are, A. Koelliker, "Handbuch der Gewebelehre des Menschen " Leipzig, 1852. 5 Auf., 1857; and besides German works, Todd and Bowman ' Anatomy and Physiology of Man," Lond., 1856. 2 vols. L Beale " TI.p Structure of the Simple Tissues," Last ed. A. Eckcr's copper plates in' WaaJr's Tcones physiologies, may also be recommended. y §4. In an earlier section we have seen that the studv of the anatomical characters of tissues is the offspring of a comparatively late era of natural and medical science. But the chemistry of the tissues, or " histochemistry " is of more recent origin still. And in that an acquaintance with'the com position of the different structures of the body can only be "ained hv iC application to them of the facts of organic chemistry, so is histochemistry INTRODUCTION. 5 in its progress dependent on the latter: in fact, it is only a special branch of the same. A lthough in the infancy of chemical study a certain amount of notice had been taken of organic bodies, nevertheless, owing to the nature of the matter to be considered, they could only be dealt Avith (scientifically speaking) subsequently to the establishment of laws relative to inorganic substances and their combinations. And only after the latter, as the simpler had been studied, and that the more important laws of inorganic chemistry had been laid doAvn, did it become possible to invade the more obscure field of organic chemistry Avith success. It must be admitted, hoAveArer, that important discoveries had been made by Scheele (1742-1786) in the latter subject. Thus a number of vegetable acids, glycerin, uric acid, and cyanic acid, had all been brought to light. But these were only details, Avhose worth from a scientific point of view it remained for a later day to demonstrate. It was only with the introduction of quantitative analysis by Lavoisier (1743-1794), and after that his contemporary, Priestley (1733-1804), had: discovered oxy- gen, that a neAv era in chemical science began to daAvn—an epoch of exact research supervening upon the overthrow of phlogistic theory. From this point on it became possible to gain an insight into chemical com- bination by means of the balance—to recognise the elements of organic bodies, to place upon a sound basis the rules of equivalent and atomic weight, and establish a foundation for a system of stochiometry. And as in microscopical anatomy the improvement of instruments led within a short space of time to a more extended acquaintance with the subject, so do we see here in the province of chemistry the dawn of an era under the sun of Lavoisier's genius, in which, by a rapid succession of discoveries, the new science attained, within a short space of time, a wonderful degree of development and cxtensiveness. It Avould be impossible, in the scope of such a work as the present, to bring in review the details of this progress in development, and we shall only mention a few points in regard to it of special interest. The first impulse was given to the study of organic substances through the "works of Vauquelin (1763-1829) and Foucroy (1755-1809). Much profit accrued also to zoochemistry through their labours in the investiga- tion of the constituents of the urine, which Avere also ably handled by Proust (1755-1826). In the year 1815 Gay-Lussac (1788-1852) dis- covered cyanogen, an organic compound Avhich conducts itself in com- bination much in the same way as an organic element. Thus he paved the way for the theory of organic radicals, to be further developed at the hands of future observers, j Many other discoveries, both in organic and animal chemistry, were made about the same time by Theuard (1777-1857), and in 1823 Clievreul published his celebrated treatise on animal fats. Modern elementary analysis (brought to such a degree of perfection at a later date) Avas first opened up by Gay-Lussac and Thenurd, and from that time on a knowledge of organic bodies, from a quantitative point of view, was rendered possible. But under Berzelius (1779-1848), the greatest chemist of his time, the whole science now made the most brilliant advance, especially in the direction of organic analysis, Avhich was pursued by him Avith all the accuracy of the present day. He was, in fact, the founder of the stochi- ometry of organic bodies, and of the definite systematised zoochemistry avo at present possess. Then the name of Mitscherlich (born 1796) must be 6 MANUAL OF HISTOLOGY. remembered as the discoverer of isomorphism. Among those who have lived in our own day, Liebig (1803-1873) may be said to have taken the place of the last-named Swedish philosopher. By his labours in the held of organic combination he has made himself celebrated, and has obtained, also in a wider circle than any other, a recognition of his genius by his imperishable popular essays on the science. He may be looked upon as the founder of the physiological chemistry and elementary analysis of the present day. Another important step towards an insight into the origm of organic substances in the body was made in 1823 by Wohler, Liebig s talented coadjutor, through his well-known discovery of the composition of urea. §5. Study of the nature of the substances occurring in the animal economy, —their properties, constitution, transformations, &c.—constitutes Avhat is termed " zoochemistry." The application of zoochemical facts to the elu- cidation of processes taking place in the system, the contemplation of the chemical features of life and significance which the elements of composition have in the same, includes, if not all, yet the chief objects of "physiological chemistry." That both these branches of study could only be carried on subsequent to the arrival at a certain degree of maturity of chemical science, is perfectly obvious, as has been already remarked, and requires no farther comment. Again, the special application of the facts of physiological and zoochemis- try to the tissues composing our frame, constitutes what is termed " histo- chemistry." Its sphere lies in the consideration of the chemical con- stitution of the '.'structural elements," and consequently also of the tissues. It is engaged Avith the substances occurring in the latter, their introduction, origin, and the significance they possess in the life of the form and tissue- elements ; it traces their metamorphosis, decomposition, and elimination. At present Ave can only boast of a very rudimentary histochemistry. In fact, we are met at all points by the most discouraging difficulties in this branch of study, owing to the nature of the subject to be dealt Avith. Compared with the extraordinary accuracy of anatomical analysis, through the aid of the microscope of the present day, the means at the disposal of the chemist for the separation of the unstable constituents of the tissues appear coarse and rude. While the histologist is able, for instance, to dis- tinguish with ease, in the most ordinary form-element the cell, envelope contents, nucleus, and nucleolus* the chemist is still unable to brina these several parts within the grasp of his analysis. Further, it is a rare thin« Avith him to succeed in the analysis even of similar structural elements for themselves, even setting aside their ultimate composition; for, oavhio- to the complex nature of most tissues, he has to deal Avith a mixture of several kinds of form-elements, Avhich cannot'be separated by chemical means After what we have just seen, too much must not be expected from the histochemistry of the present day. And yet we need not forget, in the contemplation of its necessary deficiencies, how much this special branch of science has produced. We must remember, farther, that without u knoAvledge of composition, true scientific study of histology is impossible and the latter is in danger of degenerating into a mere toying Avith details of form. And as histochemistry, on the one hand, can only be based on a clear insight into the minute anatomical relations of the tissues so does it form, on the other hand, the indispensable complement to histoWv INTRODUCTION. 7 Among those who have specially distinguished themselves in connection with this subject, Ave may mention the names of Mulder, Bonders, C. Schmidt, Lehmann, Schlossberger, Hoppe, and Kiilme. Schlossberger is the author of the first hand-book on histochemistry Avhich scientific litera- ture can produce. §6. In conclusion, we have only to give a brief sketch of the plan we shall pursue in the following pages. Histology and histochemistry combined, or the study of the finer structure and chemical composition of parts, con- stitutes the most important foundation for physiology and scientific path- ology. The whole subject may be arranged, according to our views, into three great natural divisions. In the first will be considered the matters of which the human and animal body generally is composed, Avith their histological and (as far as inseparable from these, and that a knoAvledge of them is indispensable for a proper comprehension of the whole) their physiological characters. Again, in another section of the same, the organised units of the body, the " structural or tissue-elements," Avill be brought in review, Avith their shape and composition, purposes and origin, ultimate destiny and origin, one from another. This constitutes "general histology axd histo- chemistry." In the second division—histology in the more restricted and real mean- ing of the word—the various tissues, in their anatomical relations and composition, will be brought under notice. Here also Ave shall consider the mode in which the form or structural elements of the first division are employed in the building up of certain masses. It stands to reason that here also the physiological characters of the tissues and their origin must still be frequently referred to. A third division, finally, will be devoted to the consideration of the more minute structure of the organs and systems of our body, or the man- ner in which they are put together out of different tissues. This may be termed " topographical histology." 2 THE ELEMENTS OF COMPOSITION AND OP STEUCTUEE OF THE BODY. T. ELEMENTS OF COMPOSITION. Chemical investigation has gradually brought under our notice a number of bodies, some organic and some inorganic, which enter into the formation of the human frame as elements of composition. Owing to the rapid progress of science the tale of these increases year by year. But these bodies are by no means laid down once for all in the organism to belong to the latter for the whole term of its existence, and to form permanent constituents of its fluid and solid portions. On the contrary, the material of which the animal body is composed is subject to continuous change, to constant transformations, or, in other words, is incessantly coming and going. The substances of which our body is made up—those, namely, entering into the formation of tissues—consist, together with water and other mineral matters, of certain groups of organic principles. These are the albuminous, or, as they are called, the "protein substances," and the nearer derivatives of the same, especially the glutin-yielding and elastic materials, with fatty matters and pigments. Thus we observe that the number of chemical compounds of which our frame is made up is primarily but small. But owing to the fact that these do not continue long in their original condition, but undergo decay and metamorphosis, and must in conse- quence be changed, Ave have an extensive series of chemical mutations bound up with the exitus of matter. We need not be surprised, then, if, out of this limited number of histogenic substances, a whole host of mutation or decomposition products takes its rise. The introduction also of new material to make up for waste likeAvise introduces many chemical metamorphoses. In considering, then, the elements of composition, all these points must be borne in mind. It belongs to the province of histochemistry to show by Avhat processes alimentary matters are ultimately converted into the constituents of organs and tissues, or, in other words, to follow up the formation of histogenic substances. Again, it must deal as far as possible with the question as to the nature of the numerous products of decomposition. It should demonstrate also how and by what chemical processes the latter spring from histogenic substances; what is the rela- tion of one to the other; how one mutation product takes its origin from another; and what part each plays in the occurrences of the economy, until it is finally cast out of the system. In this way only could we acquire a satisfactory knoAvledge of the chemical constitution and decay of our body. But, unfortunately, the state of science at the present day does not admit of all these requirements being satisfied in the remotest degree. 12 MANUAL OF HISTOLOGY. We are, to be sure, tolerably well acquainted with the general inter- change of matter which takes place in the system, but not so that in the individual organs. We are, indeed, justified in concluding that this in- terchange of material in the latter possesses varying degrees of intensity ; that it increases during the action of the part, and decreases during rest; but Ave are possessed of almost no facts which would enable us to de- monstrate with desirable accuracy the amount of this traffic, as it were, Avhich goes on, even in a single tissue. If in this way the destiny of many constituents of our body is veiled in obscurity, how much more so, then, their real chemical relations. Although of many substances Ave are able to say, " They are products of decomposition, residues, relics of broken down tissue, their sojourn in the body has no other significance," still, in dealing Avith others, great difficulties arise when it is to be decided to what side of metamorphosis they belong—to the formative or to the retrogressive. Of the sources of many products of decomposition we know nothing certain ; and even the changes effected by chemical action are either but very unsatisfac- torily understood, or not at all. Superfluous alimentary matter, so often present in the system, may possibly be hardly distinguishable in its derivatives from the matters resulting from metamorphosis of some con- stituents of the body itself. Finally, we are uncertain still in regard to many mineral substances, whether they are essential integral components of our body, or are only casually present in the latter. Noav it is, properly speaking, the theme of physiology to follow up this behaviour of material in detail, and to interpret its full significance for animal life; but histochemistry will be frequently obliged to enter upon physiologico-chemical research, for only in this Avay can a know- ledge of the precise nature of the substances of which tissues and organs are composed be acquired. Commencing with the axiom, that the physiological characters of a matter are in the first place dependent on its chemical constitution, we choose as an introduction to the elements of composition of the human body a section principally chemical. A. Albuminous or Protein Compounds. §8. Absent from no organism, and taking part in the construction of all tissues, these matters, which constitute the most important materials of nutrition, appear of the highest significance in animal life ; indeed thev .may be regarded with aU propriety as the chemical substrata o'f the latter. Their histogenic qualities come even more prominently before us in the embryonic body than in the mature; for in the latter many parts consist of other than albuminous substances : for instance, of collaeen chondrigen, elastic matter, and fats; whereas, in the earliest periods of existence, protein compounds are everywhere present. Those matters just named, however, must also be looked upon as derivatives of the latter, produced by metamorphosis of albuminous principles The great instability and tendency to decomposition of all the members of this group cause the appearance of a considerable number of substances in the system which m some cases participate still, though in a ndno degree, in the formation of tissues, and are in others (having under^eTo-me ELEMENTS OF COMPOSITION. 13 further modifications) to be looked upon as effete, and no longer service- able for any of the functions of life. As such, they may either circulate in the various juices of the body until eventually excreted, or may remain behind in the tissues in the character of dregs or sediment as it Avere. All protein substances are of exceedingly complex composition. They contain, beside carbon, hydrogen, and oxygen, a large amount of nitro- gen, and invariably sulphur. Phosphorus was also formerly supposed, though erroneously, to be present. Their true constitution is still quite obscure. They all become swollen and puffy when placed in water, and enter into combinations with acids and bases, but Avhether in regular propor- tion is not yet known. They dissolve in alkalies, but probably with meta- morphosis or decomposition, and may be throAvn doAvn from such solu- tions by the mineral acids. They likewise form combinations Avith acids, from which they may be again precipitated by means of the alkalies. The action of nitric acid causes them to assume a yellow hue, from the generation of an acid known as xantlioproteinic. Milton's reagent also, a solution of nitrate of mercury, containing nitrous acid, communicates a red colour to them, while iodine tinges them yelloAvish-brown. In con- centrated hydrochloric acid they are dissolved, assuming at the same time a violet tint. The action of sugar and concentrated sulphuric acid upon the protein substances gives rise to a change of colour in them, at first to purple, and subsequently to more of a violet-hue (Schultze)—a reaction which they share with the acids of the bile and with elain. In watery solutions they bend a ray of polarised light to the left. Oxidizing agents, as well as dry distillation and putrefaction, develope .in albuminous bodies a number of decomposition-products, such as formic, acetic, and benzoic acids, oil of bitter almonds, and also crystalline matters, as leucin and tyrosin. (See below.) Most of the protein substances appear in the body under tAVO isomeric modifications—firstly, in solution, or gelatinised, as in the greater number of fluids and tissues of the system ; and—secondly, in a coagulated or in- soluble state. They pass from the former into the latter condition in various ways, partly by boiling, partly by the action of strong acids, and finally, as the saying is, spontaneously. In the first modification the protein substances may be far more easily distinguished, one from the other by certain definite reactions, than Avhen in the coagulated con- dition. §9- The complex composition of the principles under consideration, their indifferent nature, and great instability, account for the fact that, up to the present, their true constitution has remained utterly unknoAvn. Indeed, we find a most discouraging obscurity resting over this most important of all groups of animal substances. So far is this the case that, in fact, we are not even able to enumerate the various albuminous principles Avith anything like certainty. Again, the great instability of the protein substances gives rise to the appearance in the organism of a considerable number of decomposition- products, to whose nature and mode of origin we are still in most cases almost complete strangers. Among these may be reckoned, as far as Ave knoAv at present, urea, uric, hippuric, and gallic acids; taurin, glycin, 14 MANUAL OF HISTOLOGY. leucin, tyrosin, sarkin, kreatin, kreatinin, glycogen, grape and milk sugar, inosit, and others besides. From a knowledge of these matters, it is not possible at present to arrive at any definite conclusions in regard to the constitution of the protein substances themselves; we may, however, set it down as being very complex. Owing to their great liability to under- go decomposition, farther, the protein compounds appear to be peculi- arly fitted to act in the economy as ferments, i.e., to effect a metamor- phosis in other substances Avithout at the same time acting through their chemical affinities. We shall refer again to these properties in § 12. Turning now to the peculiarities of the protein compounds and their formative derivatives, especially important in histogenesis, we must bear the folloAving points in mind : — ^ 1. The fact that the substances in question are not crystallizable, but ■ ' belong to the colloid group in the ordinary sense, as stated by Graham. [ This seems to constitute them peculiarly well fitted to assume the specific •-- forms of tissue elements, and to preserve the same. ^- 2. Their readiness to imbibe water, and to swell up in the latter -' into gelatinous masses, seems to render them suited for the formation of the Avatery, soft, and semi-solid matters of many tissues. Their capa- city for gelatinisation appears greatest in slightly alkaline or acid water; in solutions of neutral salts less than in pure water. 3. The remarkable readiness manifested among the protein bodies to change from one modification to another, as well as from the liquid to the gelatinous or coagulated state, and vice versa, renders them capable of becoming deposited from the animal juices in the solid form, or, when previously so laid down, of undergoing re-solution and easy transport to other localities. 4. While gelatinised protein substances admit of the passage through them of crystallizable matters, they oppose the most determined resist- ance to the diffusion of colloid materials. 5. Albuminoous principles manifest a readiness to intermix with other bodies, e.g., fats, and phosphate of lime, and to retain these with obstinacy. They may therefore be regarded as the bearers of these substances. 6. On the other hand, true albuminous substances appear unfavourably constituted to form for any length of time unchanged the elements of composition of a tissue, owing to their great unstableness. They seem to impart to the textures into whose structure they enter, a certain aptness to undergo physical change, as may be strikingly seen in many instances. This is not the case, hoAvever, Avith many of their derivatives whose liability to alteration appears to be far more limited__as for instance, keratin, chondrigen, and elastic material. These bein°- pecu- liarly suited for permanent tissues, serve for the formation of indifferent membranes, allowing the transudation of animal fluids, or including the same. ° §10. Albumen. This most important of all the protein substances in the svstem coagulates between 55° and 75° C. from its solutions in the form of flaked and not spontaneously like fibrin. From very dilute solutions it can only be separated by a much more elevated temperature. Like other protein matters it has two forms, a soluble and coagulated ELEMENTS OF COMPOSITION. 15 Of the first there are many varieties; but all these differences are probably dependent upon the admixture of other matters, such as alkalies or acids. Soluble albumen is precipitated by alcohol, mineral acids, tannic acid, and the salts of most metals. A larger or smaller quantity is also thrown down by the passage through it of a stream of carbonic acid. It becomes converted into the insoluble modification as already men- tioned by boiling; further, by the action of most acids, without, hoAvever, being always precipitated. The alkalies likeAvise transform albumen into a very insoluble substance, but do not throw it down. Albumen is not present in the animal juices in a pure state, but com- bined with a certain proportion of soda, saline Avater being the solvent. Such albumen has a weakly alkaline reaction, coagulates more in gelatin- ous masses than in flakes, and is, on the Avhole, more soluble than in the pure condition. A larger proportion still of soda may modify the coagu- lation of albumen by heat in many ways. Coagulated albumen partakes of the same nature as the remaining pro- tein substances in the same state. Entering the body with the protein substances of the food, it appears as a constituent of blood, chyle, and lymph, and also of the fluids saturat- ing various organs. Combined with some peculiar substances, it appears to form the medulla of nerves. To what extent it exists in the system in the coagulated form is a question difficult to answer in the present state of science. It can hardly be doubted, however, that it does so occur, and the finely granular contents of many animal cells are probably entirely or partially composed of it. We are likeAvise at fault Avhen asked to indicate the histogenic signi- ficance of albumen more in detail. It can hardly be doubted, hoAvever, that it is of very great importance, in that it is the first protein substance from Avhich many of tho others in the organism take their origin. §11- Fibrin, Fibrinogen, and Fibrinoplastin. Fibrin has always been described as a substance which does not coagu- late at boiling point, but, as the saying is, spontaneously, a short time after the animal fluids in which it is dissolved during life are poured out of the body. It coagulates more rapidly at a moderately high than at a low tem- perature. The oxygen of the atmosphere has probably no accelerating effect upon the process, for in the interior of the body it is observed to take place in fluids which have come to a state of rest in closed cavities. The process may be retarded by the presence in the fluid of carbonic acid, or the addition of various alkaline salts, such as Glauber salt, for instance. Coagulated fibrin can never be obtained pure, hoAvever; for, in the act of congelation, the numerous cellular constituents of the fluids in which it is contained become entangled in it. It offers, besides, many varieties for our consideration. In water acidulated with hydrochloric acid, it swells up, without, hoAvever, dissolving (Liebig); in contrast to syntonin obtained from muscle tissue (see beloAv). Coagulated fibrin is dissolved in solutions of various alkaline salts—for instance, in nitrate and carbonate of potash, when the temperature is somewhat elevated— forming a substance similar to albumen. According to Thenard, further, 16 MANUAL OF HISTOLOGY. superoxide of hydrogen is rapidly decomposed by fibrin. Fibrin may be obtained from blood, chyle, and lymph, in small but variable quantity, also from serous transudations. Let us now consider for a feAV moments the phenomena of coagulation of fibrin. Fluids in which this substance is contained become of a thickish or even jelly-like consistence soon after coming to a state of rest. Later, in consequence of progressive contraction of the fibrin, a certain quantity of the entangled fluid is squeezed out, and. the coagu- lum becomes more or less solid as it decreases gradually in size. Under the microscope a homogeneous jelly is at first perceived ; later on a tangle of usually very delicate threads or fibres (rarely broad), by which the cellular corpuscles of the fluid are caught. By many these fibres are re- garded as the optical expression of folds or rugae on fine membranous masses. In regard to the origin of fibrin, it was for a long time generally sup- posed that it took its rise from albumen. And from the fact that its analysis showed a larger proportion of oxygen than is found in the latter, the hypothesis Avas advanced that fibrin is formed by a process of oxida- tion or putrefaction from albuminous substances. Some years ago an interesting discovery Avas published by A. Schmidt, which completely upset all earlier theories as to the constitution of the material in question. According to this observer, there exists no fluid fibrin at all in the animal fluids as long as in motion. It is first generated in the blood and other liquids by the chemical combination of tAvo nearly related com- pounds, which have been named by the author ''fibrinogen" and "fibrino- plastin." The first of these (also called metaglobulin) is dissolved in the plasma of the blood; the second (or paraglobulin), Avhich, combining Avith fibrinogen, converts it into fibrin, exists, on the contrary, according to Schmidt, in the bodies of the coloured blood-cells, passing from these into the plasma. It is exceedingly similar to the globulin of these cells, (§ 12), or perhaps identical, and probably corresponded Avith the so- called "serum casein," (A Schmidt). Lymph, chyle, pus, and many tissues containing cells (but not cartilage and tendon), and also fluids into Avhich these cell-contents have passed,—as, for instance, the serum of the blood, synovia, humours of the eye, and saliva,—are all fibrinoplastic. Fibrinogen also, which is very like fibrinoplastin in its reactions—both may be precipitated from dilute solutions by conducting through them a stream of carbonic acid—appears Avidely distributed throughout the sys- tem, and is contained in almost all serous fluids, as well as those saturat- ing connective tissue and muscle. The rapid mutation of matter Avhich takes place in the moving juices of the body is supposed to be the obstacle to the formation of fibrin during life. Schmidt believes himself also justified in the conclusion that, on the chemical combination of these two '' mother substances" to form coagulated fibrin, the alkalies, which previously held them in solution, are set free. §12. Myosin. Muscle-Fibrin, or Syntonin. The contractile structures of the organism, the protoplasm of Avhich the bodies of young cells are formed, Avith striped and smooth muscle fibres, all consist of a series of albuminous substances remarkable f " ELEMENTS OF COMPOSITION. 17 peculiar reactions, as Avell as in almost all cases for the property of coagu- lating at comparatively Ioav temperatures, ranging from 35° to 50° C. One of these substances, the myosin of Kuhne, coagulates after death, and is thus the cause of rigor mortis. Coagulated myosin is not soluble in pure water, but is readily so in such containing as little as ten per cent, of chloride of sodium. It may likeAvise be dissolved in dilute acids and alkalies. It has the same action upon superoxide of hydrogen as fibrin. Beside myosin, the fluids with which muscle is saturated contain three other soluble albuminous matters, namely, an albuminate of potash, and tAvo substances which coagulate,—one at 45° C, and another at 75° C. From dead muscle, but also from other albuminous materials, a muta- tion product has been extracted by very dilute acids, to Avhich the name of muscle fibrin or syntonin has been given by Lehmann. In contradis- tinction to the fibrin of blood, it is soluble in Avater containing 0T per cent. of hydrochloric acid, but not so in solutions of nitrate and carbonate of potash. It has no effect, moreover, upon superoxide of hydrogen. Casein. This protein substance, which is probably an albuminate of potash, does not pass from the soluble to the insoluble form spontaneously, like fibrin, but on coming into contact Avith the mucous membrane of the stomach. On being heated, liquids in which it is contained become covered Avith a thin pellicle, consisting of casein modified by the oxygen of the air. Casein is precipitated by acids in flakes, and in contradistinction to albumen by acetic acid. According to Lehmann it is not thrown doAvn from milk by a stream of carbonic acid. This substance forms the chief constituent of the milk of man and the mammalia, and the most important aliment for the infant. How far it is besides distributed through the system is still uncertain; its presence in alkaline fluids, however, is very probable. It is said to exist in the middle coats of arteries by M. Schultze, Globulin. Crystallin. By these names are known certain albuminous substances coagulating like albumen when heated,. They require, however, a higher temperature, and then separate either in the form of a globular mass or milky coagulum. A solution of globulin, acidulated Avith acetic acid, is said to be pre- cipitated by careful neutralisation with ammonia, and an ammoniacal solution by acetic acid. Globulin is entirely throAvn doAvn in fluids by a stream of carbonic acid. Many things have in course of time received the name of globulin. It is found in the lens, in blood-cells (?), in the plasma of the blood, as fibrinogen and fibrinoplastin (§ 11), and in exudations. Peptones. The albuminoids entering into the composition of tissues, as Ave have just seen, do not possess the poAver, when in Avatery solution, of passing through animal membranes. They are colloids in Graham's sense of the Avord (p. 14). These, on being received into the body, partly from the animal and partly from the vegetable kingdom, are all converted by the processes of 18 MANUAL OF HISTOLOGY. digestion into what are termed peptones—i.e., easily diffusible substances of very similar or identical constitution. These peptones are by no means so easily precipitated by reagents as the colloid albuminates. Thus, in contradistinction to the latter, they are not thrown down by boiling, by dilute mineral acids, or by acetic acid. On being precipi- tated by alcohol, they may be again dissolved by watery spirits of wine. A polarised ray of light is deflected by them strongly to the left. Matters containing collagen and chondrigen, and also mucus, the con- sideration of Avhich will soon occupy us, yield Avith greater or less certainty corresponding peptones. Ferments. It has been already noticed above (p. 14), that the instability of the albuminates permits of their ready conversion into what are termed ferments. By the action of such substances,—Ave believe them at present to spring in all probability from this source; the albuminous matters are converted into peptones. The ferments appear combined Avith water as constituents of the gastric, intestinal, and pancreatic secretions. Others of them, from the mouth and salivary glands, transform amylon, dextrin, and glycogen into grape sugar. A ferment in the pancreatic juice splits up the neutral fats into fatty acids and glycerin. Decomposing albuminous substances convert urea into carbonic acid and ammonia, &c. Thus the mutation of the most important substances in the body introduces a great chemical action in the same, and leads even to the assimilation of new albuminoids in the most extraordinary manner. B. Haemoglobulin. §13. Haemoglobulin, Haematoglobulin, Haematocrystallin. We have been recently made acquainted with a remarkable substance of still more complex constitution than the albuminates, Avhich may very easily be resolved into an albuminous matter resembling globulin and into hocmatin. From the red blood-cells of man and the vertebrates generally a coloured crystalline substance may be obtained, namely, after destruction of the cells, containing iron, and of the greatest instability. Of this the blood-crystals so long known are composed (fig. 1). From the investiga- tions of the Germans Funke, Lehmann, Kunde, Teichmann, Bojanousky Rolldt, Hoppe, Bottcher, and others, we learn that the substance Avhich thus crystallizes is by no means the same in all classes of vertebrates but offers many differences for our consideration as regards solubility'and crystalline form. The difficulties of dealing with it chemically are greatly enhanced by its liability to decomposition, and its admixture with other matters. It may be obtained with greater or less ease in various ways • by first conducting a stream of oxygen through a mixture of blood and water and then carbonic acid ; then by evaporation of diluted blood, to Avhich alcohol and ether have been added upon the glass slide of the microscope Its separation is favoured by the presence of light according to the" general opinion. Crystals may likewise be obtained by the freezing and ELEMENTS OF COMPOSITION. 19 subsequent thawing of blood; by elevation of temperature to 60° C.; by electric discharges and the continuous current; by pumping out the gases of the blood; by the addition to the latter of various salts, such as sulphate of soda and those of the bile; and by the action of chloroform Avith free access of air. The blood of different animals crystallizes with varying degrees of readiness. In that of the guinea pig crystals are formed particularly rapidly. The blood of the splenic vein is also remark- able abovo that of all other localities for the freedom Avith which crystals are formed in it. There appear to be further several kinds of haemoglobin in the animal kingdom. In the Teddish blood of many of the invertebrate animals haemoglobin has also been found. The colouring matter of muscle is identical, according to Kiihne, Avith that of the blood-corpuscles. Blood-crystals are met Avith under various forms—such as prisms, tetrahedrons, hexagonal tables, andrhombohedrons. The first is by far the most univer- sally encountered, appearing in man and the greater number of mammals (fig. 1, c), in Avhich rhombic tables may also occur (b). The haemoglobin of the mouse and guinea pig assumes the form of tetrahedrons (d). Hexagonal plates have up to the present been found in the blood of the squirrel only (/). In the hamster or German marmot we find rhombohedrons (e). In fact, almost all blood-crystals belong to the rhombic system, Avith the exception of those of the squirrel, which belong to the hexagonal (Rollet, von Lang). Haemoglobin crystals are double-refracting and pleochromatic ; observed in one aspect they are bluish-red, in another, scarlet. They are insoluble in ether and alcohol, but dissolve in water, com- municating to it a blood-red tint. Watery solutions of haemoglobin coagulate on being heated, owing to the production of an albuminous substance globulin, and haematin to be mentioned beloAv. The same separation is brought about by the action of acids and alkalies. Haemoglobin combines with many gases, e.g., oxygen, carbonic oxide, and nitrous oxide. Crystals obtained under free access of air con- tain oxygen in loose chemical combination, which is parted with in a vacuum, or Avhen the former are heated- This is the oxyhemoglobin Fig. 1.—Crystals from the blood of man and some mam- mals, a, blood-crystals from human venous Wood; 6, from the splenic vein; c, crystals from the blood of a cat's heart; d, from the jugular vein of a guinea jiig; e, from the hamster; and/, from the jugular vein of the squirrel. 20 MANUAL OF HISTOLOGY. of Hoppe, to which the statements made above in respect to blood- crystals refer. 'A dilute solution of oxyhaemoglobin shows, as was discovered by Hoppe, two broad bands of absorption between the lines D and E of the solar spectrum (fig. 2, a) in the yelloAV and green part. Solutions of reduced iX /J A a-B- C D I II fl Ei 11 11 i n i m rrp-r F [ii|i|ihi|iiin'iiii|iiii|inl|i|.l||||T 2tf a e, ,la:matin in alkaline solution; /, redded n^a^lotTpSm' S&SZSfifft^™"' ^^'(^Lf^ W' haVe ^ ^ atS°rpti0n W ^ween Reduction of oxyhaemoglobin takes place easily It mav b*» w, vt about by the action of carbonic acid also J 7 ^ hl0n^ Reduced haemoglobin may also form crystals. They are of * Aa purple colour, and far more soluble than those of oxyhaemocdobin P I he latter substance, m contact with carbonic oxide cas °r>arr, m'ti, •* oxygen, and absorbs the last named compound. In this W',VV I v, S compound of carbonicoxide with hemoglobin is produced 7^)! ELEMENTS OF COMPOSITION. 21 The combination of haemoglobin with nitrous oxide (Hermann) conducts itself in a manner similar to its combination with oxygen. C. Histogenic Derivatives of the Albuminous Substances or Albuminoids. §H. Keratin. Mucin. Colloid. Wo come now to certain matters Avhich receive in general but little attention. They are related to the protein compounds, and take their origin apparently from the latter Avithin the body. They also are colloids. Their decomposition products are, in many respects, very similar to those of the albuminous substances. In the older cells of horny tissue, of epithelium, of nails and hair, as Ayell as in the analogous structures of animals, there exists a mixture or compound difficult to isolate in a pure state, and insoluble in water. It may contain up to five per cent, of sulphur, and is partially soluble in alkalies. Its decomposition products, among Avhich leucin and a large quantity of tyrosin are found, indicate a close relationship with the pro- tein substances. To this compound the name keratin has been given. Under the name of mucin is knoAvn a substance, sometimes gelatinous, sometimes dissolved, which occurs in the secretions of the mucous mem- branes, in synovia and the vitreous humour of the eye, in the gelatin of Wharton of the umbilical cord, in several connective-tissue structures, and finally, in certain pathological products (mucous tissue). This substance does not coagulate on being heated. It is thrown doAvn in flakes by acetic acid, and is not redissolved by an excess of the same. Alcohol produces a species of stringy coagulum in solutions containing mucin, but this dissolves again in warm Avater. In many other respects mucin resembles the protein compounds ; its reaction Avith sugar and sulphuric acid is also the same. It appears to contain no sulphur, but is, on the other hand, rich in phosphate of lime (Scherer). Mucin, which is not diffusible, manifests fermenting properties. It appears to form a kind of peptone (Eichwald). Colloid matter may also be mentioned here : a usually homogenous substanco of some consistence, insoluble in acetic acid, but not, like mucin,,precipitated by the latter. It is soluble, on the other hand, in alkalies. It is generally met Avith as a pathological product of the transformation of tissues (colloid degeneration), but also normally at cer- tain periods of life, particularly in the thyroid gland of man. §15. Substances yielding Glutin. From experience, Ave knoAV that the important group of glutin-yield- ing materials takes its origin from protein compounds. These principles only occur in animal organisms, and constitute a large part of our body, in the form of interstitial matter in structures composed of connective tissue, of bone, and of cartilage. We understand by glutin-yielding materials, compounds containing nitrogen and sulphur, completely in- soluble in cold Avater, but Avhich may be rendered soluble by prolonged 22 MANUAL OF HISTOLOGY. boiling in the same—yielding then a principle which becomes gelatinous on cooling, known as glue. It is supposed that in these processes the composition of the materials under consideration is not essentially altered. Our knowledge of the chemistry of the formation of glue is not, hoAV- ever, at all satisfactory at present. From allied protein substances these materials differ in their solubility in boiling water and subsequent gelatinisation. With the sugar and sulphuric acid test, likewise, they do not become red, but yellowish- brown. With nitric acid they assume a yellow colour, like albuminous materials. All efforts to convert albuminous matters into glutin-yielding sub- stances artificially, as well as the latter into one another, have up to the present proved futile. Collagen and Glutin. Collagen, or the substance converted into ordinary glue or glutin by boiling, has received but little attention, while glutin has been made the object of extensive investigation as regards its reactions. A solution of glue is not affected by mineral or acetic acids, or by alkalies ; tannic acid alone gives a copious precipitate. Among the earthy and metallic salts, the chlorides of mercury and platinum, and basic sulphate of iron, pre- cipitate glutin, but not acetate of lead. A polarised ray of light is bent to the left by a Avatery solution of the matter in question. With man- ganese and sulphuric acid it yields the decomposition products of albumen; with acids and alkalies, ammonia, leucin, glycin, and other compounds. From glutin is formed the extensive group of connective-tissue struc- tures, the organic substratum of bones and ossified cartilage. Conse- quently collagen is found Avidely throughout the body, entering into the composition of tissues of low physiological dignity. From the fact that, with one exception, that of leucaemic blood (Scherer), no glutin has as yet been found in the fluids of the body, we infer that collagen must spring from the protein substances. Connective tissue likewise, at an early embryonic period, yields no glutin, but appears to consist of a protein compound (Schwann). As to the mode in which the necessary changes here take place, the present state of zoochemistry does not admit of an answer being given. Chondrigen and Chondrin. Chondrin, or cartilage-glue—obtained from the cornea, from per- manent cartilage, from bone cartilage before the commencement of ossification, and likewise from a pathological groAvth, enchondroma__is allied to glutin. Most acids, however, produce precipitates in a solution of chondrin, Avhich are again dissolved by an excess of the reagent. The precipitate, however, caused by acetic acid does not redissolve. Watery solutions of chondrin possess greater power of left-sided polarisation than those of glutin. Heavy precipitates are also seen here on the addition of alum, suhohates of the protoxide and sesquioxide of iron, sulphate of copper, neutral and basic acetate of lead, nitrate of silver, and nitrate of mercury. Boiled with hydrochloric acid, or digested in gastric juice chondrin yields, besides numerous other products, a sugar (cartilage sugar), as far as Ave know, non-crystallizable, but capable of fermentation. If this last statement be correct, chondrin may be regarded as a nitro- ELEMENTS OF COMPOSITION. 23 genous glycosid, giving «ome indication as to the constitution of the albuminates. With sulpnuric acid chondrin only yields leucin appa- rently. Of chondrigen but little is known. As to the origin of chondrin from the protein substances, the same may be said as of glutin. In regard, however, to a transformation of chondrin into glutin during the process of ossification, spoken of by some, but rather improbable, the present state of chemistry permits of no definite conclusions being drawn. It would appear that other matters nearly related to these tAvo better knoAvn glue-yielding substances may also occur in the body. Elastic Material, Elastin. In numerous tissues of the body a substance destitute of sulphur is met Avith, Avhich, unlike the glutin-yielding materials, is remarkable for its great insolubility and unchangeableness. This elastic substance, even on prolonged boiling, yields no glutin, if completely free from connective tissue. It is likewise unaffected by acetic acid, Avhether Avarm or cold. It may be dissolved, hoAveArer, by a boiling concentrated solution of caustic potash, and by cold sulphuric acid; also gradually, by saturated nitric acid Avith the formation of xantho- proteinic acid. Elastin is not coloured red by the test of sulphuric acid and sugar. As decomposition products under the action ofthe last-named acid, we find leucin, but neither tyrosin nor glycin. Elastin, the definition of which presents many difficulties also to the microscopist, enters into the formation of fibres, plates, and limiting layers in connective tissue. It forms also in various organs possibly, both follicles and tubes, and capsules around animal cells, without being a constituent of the true cell-body itself. The great unchangeableness ot this substance, Avith its chemical inert- ness, seem to render it peculiarly fitted to include the fluids of the system, and to act at times as a filter for the same. Its great elasticity also serves many purposes. Its source is not as yet known Avith any degree of certainty. There can be hardly any doubt however that it has its origin from the protein compounds of the body. D. The Fatty Acids and Fats. §16. Fatty acids appear in our body either free or combined Avith an inorganic base (fat-soap), or as a mixture of jdycerin-ethers (neutral fats). Let us glance for a moment at the latter :—'" (OH Glycerin, C.,H803 or C,H5 \ OH * (OH. Glycenn, a triatomic alcohol, with the radicle glyceryl = CAT-, is met- with as a colourless, non-crystallizable syrup, miscible with water in all proportions. Before going further, let us consider for a moment glycerophosphoric 3 24 MANUAL OF HISTOLOGY. acid, having the empyrical formula CH.PO,. It is a bibasic ether-acid of glycerin. c3h5|oh 3 (R04Ha. Glycerophosphoric acid is to be found combined with various matters —in the yelk of the ovum, in cerebral substance, and in the bile. (Comp. § 20, Lecithin.) The neutral fats, however—those glycerin ethers already mentioned above—are the compounds of most ordinary occurrence and greatest importance in the system. From the fact that in our tfn'-atomic alcohol, 1, 2, or 3 atoms of H of the hydroxyl may be replaced by the acid radical, Ave have derived three series of fats knoAvn as monoglycerides, diglycerides, and triglycerides. The neutral fats occurring naturally belong only to the last group— the triglycerides of many acids. Glycerin finds its Avay into the body Avith the neutral fats of the food. It becomes free upon the saponification of these, and must again re-combine Avith the fatty acids on the formation of fats in the tissues, occurrences in regard to Avhich we are still in the dark. The physio- logical decomposition products of glycerin are also still obscure. §17. The fatty acids of the system belong to two natural series, of which one is arranged after the formula, CnH2B02; the other C„H2„_202. Among the numerous monobasic acids of the first group, some of the lower or fluid fatty acids do not possess the characters of tissue elements, but rather those of decomposition products. Formic Acid, CH202. Has been met Avith by Scherer and Miiller in the fluids Avith which muscle, the brain, and the spleen are saturated ; also in the thymus gland (Gorup-Besanez), in sweat in considerable quantity (Lehmann), and the blood of dogs after a prolonged sugary diet (Bouchardat and Sandras). It is also found pathologically in blood. Many of these statements ap- pear, hoAvever, questionable. Acetic Acid, C2H402. Is a constituent of the juices of muscle and the spleen (Scherer). Further it is to be met Avith in the thymus gland, and has been observed in the perspiration. Acetic acid is also known as one of the ingredients of the gastric juice; it occurs probably also in the fluids of the brain. Finally it appears as an occasional constituent of the blood after brandy pota- tions. v Butyric Acid, C4H802. Appears in flesh and the juices of the spleen (Scherer); also in the milk sweat, and secretions of the sebaceous follicles of many parts of the bodv' as, for instance, on the genitals: in the urine also (?). Its presence in blood seems doubtful (Lehmann). It is found also in the contents of the ELEMENTS OF COMPOSITION. 25 stomach and intestines, as a product of the fermentation of hydro- carbons. ( 0. CJBLO With glycerin as tributynn, — C3HB -J 0. C4H70 it is a constituent ( O.C4H70 of neutral butter fat. Capronic, C8Hl202. Caprylic, C8H160j. Caprinic, C10H20Os. Acids. These are met Avith, in a free state, with glycerin, as constituents of butter, and possibly also of sweat. Among the higher members of the group Avith which we are engaged, there occur several of these acids (usually solid at the ordinary tempera- ture of the body) as constituents of the neutral fats, and consequently as histogenic compounds. They are introduced into the system Avith the fats of the alimentary matters as a rule. Their physiological decom- position probably results in the production of carbonic acid and Avater by oxidation, at the same time that the series is split up into lower members. Palmitic Acid, ClcHMOs. Palmitic acid is an element in almost all fats of the vegetable and ani- mal kingdom. Its melting point is about 62° C. It crystallizes in glit- tering pearly scales. This acid forms with glycerin a compound occurring naturally and abundantly in human fat, as (O.Cl6H810 Tripalmitin, C8H„ < 0. C,6H3tO. (O.C16H310. Stearic Acid, C18H3602. This is also a widely-spread constituent of the animal neutral fats, and is present in the human body. Here, however, it is exceeded in quan- tity by palmitic acid; but it preponderates, on the other hand, in more solid suety fats, as those of cows and sheep. Its melting point is higher than that of the preceding acids, being about 69° C. It crystallises in white silvery needles or scales. ' Its neutral combination with glycerin is known as (O.C,8HM0 Tristearin, C3H5 \ 0. 018H35O (0.C18H350. Among the acids of the second group there is only one of any import- ance in the human economy, namely— Oleic Acid (Elaidic Acid), CiBH,4Oa. Pure oleic acid is met with as a fluid which stiffens into leaves at a temperature of - 4° C. It is scentless and tasteless, and cannot be volati- lised Avithout decomposition. Its salts are not crystallizable. Elaidic acid is found as a most important constituent of the neutral fats of the body, combined Avith glycerin, namely, as 26 MANUAL OF HISTOLOGY ( 0 . C18H330 Triolein, C3H51 0 . C18H330 (0.C18H330 and also saponified Avith alkalies. It is introduced into the body Avith the neutral fats of the food. Its physiological decompositions are probably manifold. Remarks.—It was formerly believed that margaric acid was the most widely-dis- tributed of all animal fats. From the fact, however, that a mixture of equal parts of palmitic and stearic acids has naturally the same composition as margaric acid, U17H3202, some have denied the existence of the latter altogether, but incorrectly, for it has been produced artificially (Becker, Heintz). It is still a matter of doubt, however, whether it and trimargarin are constituents of the ordinary fats of the body. §18. In the foregoing section the constitution of the nmtral fats Avhich occur naturally, have been brought before our notice ; Ave have also alluded to the different fatty acids of these compounds. It is not possible to separate one from the other, with any degree of accuracy, the individual neutral fatty combinations Avhich occur here, so that our acquaintance with the latter is very unsatisfactory. They receive their peculiarities from the fatty acids of the combination. Neutral fats, when pure, are colourless, without odour, and tasteless. Their reaction is neutral, they are lighter than Avater, and bad conductors of electricity. They are insoluble in water, but soluble in warm alcohol and in ether. They give rise to fatty stains upon paper, burn with bril- liant flame, and cannot be volatilised without decomposition. By the action of steam, heated up to 220° C, the neutral fats are split up into acids and glycerin. The same effect is produced through the agency of ferments, as, for instance, putrefying protein compounds. Ex- posed to the air they greedily absorb oxygen, and with this and the com- bined action of ferments, become rancid, water being absorbed and glycerin and fatty acids set free. Further, by the action of alkalies in the presence of water, they are decomposed and converted into soapy compounds in which process glycerin is set free, while the acid combines with the inor- ganic base. It has been already remarked above, that the separation of the several neutral fats from the natural fats of the human body is not possible Hence the questions in regard to their nature have been answered in various ways Berthelot, following up Pdouze, has recently composed the neutral fats by artificial means out of glycerin and the fatty acids, and has thus opened up a new way for the recognition of the fatty matters occurring in the system. From the correspondence between their properties and those of the natural fats, many of these compounded neutral fats have been recognised as constituents of the body. f S"? T ,thrf°r?' *? Sf ^T' combina^ns, in which the three atoms of H of the hydroxyls of the glycerin are replaced by the corresnondir," radicals of those fatty acids. Thus we have a compound corre oond n! with elaidic acid, triolein a fluid at ordinary temperatures, and then hold ing two other solid crystalline neutral fats in solution, namely trivalmftt and tristearin* It is still doubtful whether we have here all thl stituents of the mixture of neutral fats occurring in the system. In butT" * To these may be added probably trimargarin. ELEMENTS OF COMPOSITION. 27 there exists a combination of butyric, caprinic, caprylic, and capronic acids, Avith glycerin. According to the quantity of solid neutral fat dissolved in the triolein, are the animal adipose tissues soft, or hard and suety after death. During life, however, owing to the natural warmth of the body, they all remain soft, and more or less fluid. In one and the same animal, moreover, the adipose matter of many parts of the body may contain variable quantities of solid fats. The neutral combinations of the latter occur Avidely distributed through- out the body. They are to be met Avith in nearly all fluids and tissues accompanying all the protein compounds and histogenic substances. Their amount is very variable. They appear in enormous quantities in the cells of fatty tissue, under the skin, in the orbit; around the heart and kidneys, and in bone; likewise in medullary nervous matter, together Avith some special compounds, now better known than formerly. Its constant presence in the tissues leaves no doubt as to the histogenic nature of fat. On the other hand, other tissues are frequently destroyed Avith fatty infil- tration or generation, both physiological and pathological (fatty degeneration). The histogenic significance of the fats appears greatly heightened when Ave remember the fact that the hard crystalline combinations forfeit their crystallizability on becoming dissolved in triolein. Under certain circumstances, solid fat separates from the natural fatty matters of the body on the cooling of the latter after death, in the form of needle-shaped crys- tals or groups of the same (fig. 3). These are known to the microscopist as margarin •rystals. Remarks.-The percentage of fats in different tissues is-in lymph, 0-05 ; in chyle, 0-2 blood, 0-4; cartilage, 13 ; bone, 1-4 ; lens, 2'0 ; liver, 2;4 ; muscle, 8'3 ; brain, 8-0; nerves, 22"1 ; spinal cord, 23-6 ; fatty tissue, 82-7 ; yellow marrow of bones, 96-0. Fig. 3.—Crystals of margavin. a, single needles; b, larger groups of the same; c, groups of needles within fat-cells; rf, a fat-cell quite free of them. §19. In considering the objects for Avhich fat is designed in the human system, the following points may be borne in mind :— 1 The fats appear important, owing to their soft, fluid consistence at the ordinary temperature of the living body, as distributors of pres- sure, as pads and filling-up matters in various positions. 2. Large collections of neutral fats, as bad conductors, prevent to a certain extent loss of heat to the system. . 3 They possess the somewhat subordinate property of rendering many hard tissues, such as epidermis and hair, pliant and soft, by satu- rating them. For this purpose the secretions of the sebaceous glands appear particularly designed. 4 Their Avant of affinity for water seems to render them peculiarly suited to separate from watery fluids in the form of granules and drops, and so "ive origin to the formation of elementary molecules and vesicles. 28 MANUAL OF HISTOLOGY. 5. Owing to a certain chemical inertness in fat, the latter appears fitted for the formation of tissues Avhich take but little active part in the chemical processes of the economy. 6. By the fermenting action of the protein compounds, but more by contact Avith the oxygen of the atmosphere, the fats become decomposed, and the fatty acids formed into other combinations, the final result of Avhich is the production of carbonic acid and Avater. The heat which is evolved in this process constitutes them of the highest importance. 7. According to Lehmann, the fats possess the nature of ferments, in that Avith the protein compounds they lead to the generation of lactic acid in fluids containing sugar and starch. The energy of pepsin in the gastric juice is also said to be increased by the presence of fats. 8. Though the neutral fats are not soluble in the Avatery fluids of the body, their soapy combinations are, and are consequently of great im- portance for the distribution of fatty acids through the system. The neutral fats are received into the body Avith food, although the possibility of their production also in the human organism from hydro- carbons must also be granted. That this takes place in many animals has been proved, as is Avell knoAvn, by Liebig. Their origin from protein compounds can likeAvise be no longer really doubted. §20. Cerebral Matters, Cerebrin and Lecithin. Among the substances of which the brain and spinal cord are made up (but also in other parts of the animal body) there occur several peculiar, unstable compounds, difficult of analysis. They are remarkable for the property of sweUing up in hot water into a substance like starch, for their solubility in warm alcohol and ether, and for their occasionally containing phosphorus. They were formerly erroneously designated as phosphorous fatty matters. Cerebrin, C^H^NO,. Cerebrin originally described by Fr6my as cerebric acid, and after- wards investigated by Gobley and Mailer, is a white powder, seen under the microscope to be composed of roundish globules. It can only be dis- solved in warm alcohol and ether, and is decomposed by boiling hydro- chloric and nitric acids It is insoluble in ammonia, caustic potesh and baryta water, and also in cold water; while in hot as already men- honed it SAvells up into a substance resembling boiled starch On being boiled with acids, cerebrin yields a species of sugar and i^ therelore a glucoside. Its precise nature remains for further ln^- Lecithin, C42H84NP09 . This substance, first discovered by Gobley, is indistinctly crvstallinp It resembles wax, may be easily melted, and is soluble \J i f i ■? i ELEMENTS OF COMPOSITION. 29 i c\\\ may be split up into neurin, (cholin) = C2H4 < -vynH \ (\tj palmitic and oleic acid, and glycerophosphoric acid. Lecithin may be' derived from glycerophosphoric acid, in which the two hydroxyl hydrogens of the glycerin are replaced by the radicals of palmitic and elaidic acids, at the same time that the neurin (half alcohol and half base) forms Avith the glycerophosphoric acid an ether-acid. Its formula is therefore C3H3 O.C, «H310 O.PO H3,0 (OH O.C2H4(CH3)3^.OH This substance, besides being found in nervous tissue, is also found in the yelk of the eggs of hens, in the blood-corpuscles, in bile, semen, and pus. There appear to be various kinds of lecithin in nature. Protagon, a substance described some years ago by Liebreich, is simply a mixture of cerebrin and lecithin. By myelin, as described by Virchow, Ave understand a substance of peculiar microscopic appearances occurring in different parts of the body, especially in those undergoing decomposition. It has a characteristic dull lustre (fig. 4), and is usually met with in masses of roundish, oval, filiform, looped, or lobulated figure, with double outline. Myelin is tinged slightly broAvn by iodine, while in concentrated sulphuric acid it becomes of a red, or at times violet, colour. It resembles cerebrin and lecithin in its property of absorbing hot Avater, and SAvelling up into a gelatinous mass, and also in its rela- tions of solubility to alcohol and ether. Myelin drops, however, may be obtained from compounds of quite a different nature, as, for instance, from oleic acid and ammonia (Neubauer). Myelin is therefore chemically untenable as a special combination. Another allied substance, knoAvn as amyloid, may be also mentioned here. This appears in peculiar homo- geneous masses of dull lustre, and is probably a mixed Fig. 4.—Different forma degeneration product of many, especially glandular por- ° myein- tions of the body (Avaxy or lardy degeneration). Amyloid matter is coloured of a peculiar reddish-brown or broAvnish- violet Avith a solution of iodine, Avhich turns to violet usually on the subsequent addition of concentrated sulphuric acid, or, more rarely, to blue. We turn finally to the corpuscula amylacea, round or bilobular structures of very variable size, which bear a strong resemblance to granules of starch, Avhence the name. They are sometimes laminated, sometimes not, and vary in their re- actions, becoming violet under the action of iodine and sulphuric acid, but frequently blue or bluish *■»*£ Avith iodine alone. Thus they resemble amylurn in one respect, and cellulose in another, although we are not justified in re- ferring them to either of these substances. The corpora amylacea are to be found in the nervous centres of putre- fying corpses, and, moreover, in quantity increasing Avith the advance of Corpuscula amylacea from the human brain. 30 MANUAL OF HISTOLOGY. decomposition. Besides, however, they may occur pathologically in the living bodv, e.g., in the organs just mentioned, the brain and spinal cord, whose sustentacular connective tissue may contain them in abundance. They are met with also in the prostate of considerable size. Remarks.—Strecker in the Zeitechr, fur Chemie, 1868, S. 437. §21. Cholestearin, C"H« J 0 + H20 . Sensible of the difficulty of appropriately grouping animal substances, for the present we insert here monatomic alcohol, with the distinct charac- ters of a decomposition product. This compound (fig. C) has a very characteristic crystalline form; it is found, namely, in extremely thin, rhombic tables, whose obtuse angle is 100° 30', and acute, 79° 30', according to C. Schmidt. These are usually arranged overlapping each other, and are frequently broken at the corners. Cholestearin is completely insoluble in water, but perfectly soluble in boiling alcohol, ether, and chloroform. It is dissolved in fats and ethereal oils; in the two combinations Avith soda of the biliary acids and in soap-water—important proper- ties in regard to the occurrence in the human body of this otherwise insoluble substance. Treated with sulphuric acid, crystals of cholestearin become of a rusty or purple colour, beginning at the edges. In concen- trated acid, on the other hand, they dis- Fig. 6.—crystals of cholestearin. S(Hve gradually, forming coloured globules. The addition of iodine to these reagents produces more lively colours still. Cholestearin, which has been recently met with widely distributed throughout the vegetable kingdom (Beneke, Kolbe), has no histogenic pro- perties, its crystalhzability seeming to render it but little fitted to enter into the structure of tissues. It possesses entirely the nature of a mutation pr(?UC^ t eF °f the fats or of azotised h^togenic substances is still undecided It is extensively distributed throughout the system, but is only excreted m minute quantities, so that some further decomposition .still quite unknoAvn to us may be inferred It is found in the blood but in small amount, and in most of the animal fluids especially m bile, but not in the urine. It is also met Avith in the substance of the brain, as a constituent of myelin, Lpatholo gical fluids andtumors, and in biliary calculi. Passing off aS the bde, it is found m the excrements. ° E. The Carbhydrates. §22. These substances bear this not very hatmilv ^ constitution of uric acid; its being the source, how- Fig. is.—Acid urate of ever, of urea, allantoin, and oxalic acid, and, according to Strecker, of glycin, renders it of great interest, and shoAvs its import- ance. Uric acid, as its name denotes, is a constant constituent of human urine. It is present in the latter, hoAvever, in far smaller quantity than urea, amounting only to about one per thousand, and combined Avith soda more- over. It is also met with, though in smaller proportion still, in the urine of carnivorous mammals. Traces only of it are found in the urine of phytophagous animals. Its amount in human urine appears to vary 38 MANUAL OF HISTOLOGY. but little according to the nature of the food taken, but much in certain morbid conditions. Uric acid is besides a constituent of blood (Stranl, Lieberkuhn, and Garrod). It is also found in the fluids with which many organs are saturated; as, for instance, that of the bx&m (Mutter), ot the kidneys and lungs in the ox (Cloetta); and in man, of the spleen (Scherer and Gorvp-Besanez). Uric acid is a mutation product of azotised tissue-constituents, and as such is widely distributed throughout the animal kingdom. As to its mode of origin, Ave.are unable to point it out, owing to our ignorance of the nature of the matter itself. The fact, already mentioned, that the injection into the body of this acid increases the amount of urea in the urine (Wohler and Frerichs), seems to point it out as the source of the latter in the system : and the purely chemical decompositions of uric acid, also, Avhich so fre- quently lead to the formation of urea, appear likewise to confirm this view. Hippuric acid is a C,KN0o §2"6. Hippuric Acid, C9H9N03. glycin (see beloAv), i.e., an amido-acetic acid = N, or ±J (CH2 / C02H in Avhich one atom of the hydrogen is replaced by benzoyl (the radicle of benzoic acid), C6H5CO, thus— H) C6H,CO } N. CH.J . COJI This acid, which takes its name from its occurrence in the urine of horses, has the primary crystalline form of a vertical rhombic prism, and sepa- rates from hot solutions in small spangles, or large obliquely streaked four-sided pillars, Avhich have two end surfaces (fig. 16). By slow evaporation from ddute solutions, crystals (b) may be obtained resembling in many respects those of phosphate of magnesium and ammonium, to be described presently. Hippuric, which has much stronger acid properties than uric acid, may be dissolved in 400 parts of cold and easily in hot water. It is also soluble in alcohol, but only slightly so in ether. It forms with alkalies and alkaline earths crystalline salts soluble in water. As to the numerous decomposition products of the acid with Avhich we are engaged, the most characteristic is the transformation which it undergoes on being heated with acids and alkalies : it is split up, namely, into benzoic acid and glycin after taking up Avater (Dessaignes). ° Fig. 16.—Crystalline forms of hippuric acid. a, a, prisms; b, crystals formed by slow evaporation, and resembling those of phos- phate of magnesia and ammonium. ELEMENTS OF COMPOSITION. 39 The same effect is produced by animal ferments in the presence of alkalies (Buchner). Like the acids Ave have just been considering, hippuric is nowhere found in the vegetable kingdom. It is doubtful whether it exists in the blood of vegetable-feeding mammals and that of man (Robin and Verdeil). It appears in human urine in about the same quantity as uric acid, though in larger amount in certain diseased states of the system. The proportion of hip- puric acid in the urine of phytophagous animals is greater, as, for instance, in ■ that of the horse. Up to the present this acid has not been met with in the juices of the organism; it has, hoAvever, been found in the scales of a skin disease knoAvn as ichthyosis. It is a fact of great interest, that'ben- zoic, kinic, and Cinnamic acids, Oil of Fig. 17—Crystals of benzoic acid. bitter almonds, and of tolu, introduced into the stomach, are excreted as hippuric acid through the kidneys. Hippuric acid possesses the nature of a decomposition product of azotised substances of the body. The fact that on the oxidation of pro- tein substances by permanganate of potash, a great quantity of benzoic acid is developed, is in favour of this view. §27. Glycocholic Acid, C26H43N06. This, which belongs to the bile, is of analogous constitution to hippuric acid, splitting up like the latter into glycin and a non-nitrogenous acid, known as cholic acid. Let us consider this latter in the first place :— Cholic, or cholalic acid of Strecker, C24H40O5, crystallizes from ether with two equivalents of water of crystallization in rhombic tables ; from alcohol with five molecules of Avater in tetrahedrons; or more rarely, in square octahedrons, which effloresce when exposed to the air. This acid is insoluble in water, but very soluble in alcohol and ether. With sulphuric acid and sugar it becomes of a purple-violet colour. The con- stitution and origin of cholic acid has not been fixed as yet. Let us now return to glycocholic acid. This crystallizes in very fine needles, which may be heated to 130° C. without under- going change. It is tolerably soluble in Avater, very easily so in alcohol and alkalies, but insoluble in ether. It may also be dissolved cold, and without decomposition, in many mineral acids, as, for instance, Eg m—Crystals of cholic acid. sulphuric and hydrochloric, but also in acetic acid. With sugar and sulphuric acid it gives the reactions of cholic acid. It is monobasic, and forms partly crystalline, partly amorphous salts, soluble in spirits of wine. On being boiled Avith potash ley or baryta Avater it is split up Avith 4 40 MANUAL OF HISTOLOGY. Fig. 19.—Crystals of glycocholate of sodium. 32K r^ E. t£ ^A'&c&ZZ Sb'cin. Among its salts one in particular must be borne in mind, namely, Glycocholate of Sodium, O^H^aNO,.. (Fi<* 19) a compound easily soluble in water? which, precipitated from its solution in alcohol by means of ether, crystallizes in large, brilliant white stellate groups of acicular crystals. This acid forms an essential constituent of human, as well as most mammalian bile. It is combined with sodium, even among the vegetable feeders. Taurocholic Acid, C26H44NS07. This second acid is related very nearly, as regards its chemical consti- tution, Avith the foregoing. It splits up, however, into cholic acid; and (instead of glycin) taurin, an indifferent substance, containing sulphur, and no longer basic. This is the amide of isethionic acid or sulfethylemc acid = C2H4 {^ Taurocholic acid, which is very easily decomposed, is non-crystallizable, but exceeds the last acid in its solubility in water and stronger acid properties. It dissolves fats, fatty acids, and cholestearin with great readiness. With sugar and sulphuric acid it gives the same reactions as glycoholic acid. Its combinations Avith alkalies are very soluble in alcohol and water, but insoluble in ether. Eetained for a long period in contact Avith ether, they crystallize. They burn with a brilliant flame. As regards the decomposition products of this acid, they are, as has been already mentioned, analogous to those of the foregoing. On being boiled with alkalies taurocholic acid splits up, on the absorption of water, into cholic acid and taurin; while, with the mineral acids, choloidinic acid besides taurin is produced, analogously to the previous case. Combined with sodium taurocholic acid forms the second chief con- stituent of the bile of man and numerous mammals, namely, tauro- cholate of sodium, C2SH43Na]S"S07. H. Amides, Amido-Acids, and Organic Bases. Under these names we have uoav to consider a series of further decom- position products. Urea or Carbamide, CH4lSr20, or CO j ^» Carbamide, Avhich, like all the rest of the substances under considera- tion here, is absent in the vegetable kingdom, but which forms, on the other hand, the chief constituent of the urine of the human body, is of perfectly neutral reaction—corresponding in this respect with kreatin, glycin, and leucin—to be referred to presently. It crystal- lises in long four-sided pillars, terminating at either end in two facets (fig. 20). It is quite soluble in water and alcohol, hut not so in ether. ELEMENTS OF COMPOSITION. 41 Urea combines with oxygen acids, forming salt-like combinations, in which one molecule of water is always present ; thus it is with nitric and oxalic acid. These tAvo combinations are of par- ticular importance in the recognition of urea, owing to their characteristic crystalline form. Nitrate of urea, CO(NH2)2,HKOa (fig. 21, a a), crystallizes in pearly scales or glittering Avhite leaves, Avhich appear under the microscope in the form of rhombic or hexagonal tables. Oxalate Of urea, 2CO(NH2)2, H2C204 + 2H20 (fig. 21, & &,) appears to the naked eye in the form of long thin leaves or prisms, found under the microscope to be made up of hexagonal tables as a rule, but also of four-sided prisms. Both salts belong to the monoclinic system. Urea combines also with metallic oxides and salts, as, for instance, with chloride of sodium. Fig. 20.—Crystals of urea, o, four-sided pillars; b, indefinite crystals, such as are usually formed in alcoholic solutions. Fig. 21.—Crystals of combinations of urea with nitric and oxalic acut a a, nitrate of urea; b b, oxalate of the same. As regards its decomposition, urea may be artificially split up on absorbing water into carbonic acid and ammonia. The same change is brought about by contact Avith animal matters undergoing putrefaction, such as protein compounds, or mucus, &c. It is OAving to this fermentation that urine becomes after a time alkaline on being exposed to the air. Urea may be obtained from other alkaloids, such as kreatin and allantoin, by treatment of the latter Avith alkalies; further, by subjecting uric acid to the action of oxidising acids and caustic potash. Urea may be produced artificially in many Avays besides. Carbamide appears in human urine as the most important of all its solid constituents. It amounts to from about tAvo and a half to three per cent. 42 MANUAL OF HISTOLOGY. of the fluid excreted, and is carried out of the body daily m con- siderable quantity. It is found likewise in the blood in very minute quantity (Strahl and Lieberkuhn, Lehmann, Verdeil, and Dolljuss), and in the chyle and lymph of mammals (Wurtz). It is also stated, but with uncertainty, by Millon, to be present in the aqueous humour of the eye. Further, it has been met with in the brain of the dog (Staedeler), and in normal sweat, according to Favre, Picard, and Funke. Under certain diseased conditions it may appear very widely distributed through- out the system. Urea, like all allied substances, a decomposition product, and unfit, owing to its solubility, to take part in the formation of tissues—springs, as we knoAV by experience, from the nrotein compounds of the system ; from those albuminous substances entering into the constitution of tissues, as well as those received into the blood from the food, and super- fluous there. Thus the amount of urea in the body is increased by muscular exertion and abundant fleshy diet; the introduction of many alkaloids into the stomach has the same effect, as, for instance, thein, glycin, alloxantin, and guanin. Finally, the injection of uric acid into the circulation causes an augmentation in the amount of urea excreted with the urine (Wohler and Frerichs). In regard to detail, we are still in the dark as to the formation of urea in the body. We do know that it is a decomposition product of the protein compounds, and also that almost all the nitrogen which leaves the system passes out in this Avay ; and yet, on the other hand, as to the chemical mutation series Avhose end factor is urea, we are in possession of but few facts. Tavo points, however, may be alluded to as throwing some light upon the origin of the substance in question, namely, that kreatin, a mutation product of the protein compounds, splits up into sarkosin and urea under the action of alkalies; and again, urea may be obtained from guanin, among other substances, by treatment Avith oxidiz- ing reagents (Strecker). But in this respect the presence of uric acid is probably of greater importance as a source of urea in the system—urea being one of the usual decomposition products of the same, derived from its oxidation. §29. We turn now to three substances closely allied one to the other to be regarded as members of a mutation series of histogenic matters, and which possibly lead to the formation of uric acid in their further physiological transformation. They are compounds very insoluble in water, but Avhich dissolve readily in alkalies and acids, forming Avith the latter crystalline salts which are partly decomposed by water. All three evaporated with nitric acid, form yellow substances Avhich, on the addition of potash without heat, assume a red colour, turning to a lively purple on the temperature Fig. 22—Crystals of chlorate of guaain. being raised. ELEMENTS OF COMPOSITION. 43 Guanin, CsHsNtO. Guanin, discovered by linger in guano, forms with hydrochloric acid a crystalline salt, met with in obliquely pointed needles or parallopipedic tables, belonging in general to the clinorhombic system (fig. 22). Some years ago Strecker obtained xanthin from the transformation of guanin. Guanin is not a constituent of urine, but is found in the pancreas. Hypoxanthin (Sarkin), C5H4N40. Hypoxanthin of Scherer, which is identical with sarkin, investigated subsequently by Strecker, is seen, by comparison of their respective formula, to be nearly related to guanin, as well as to the substance we are about tc allude to, namely, xanthin. The crystalline forms of their nitric and hydrochlo- ric acid salts (fig. 23) are characteristic, especially the first. Nitrate of sarkin, on rapid separation, forms rhomboidal plates; slowly deposited, it is met with in tufts of obliquely pointed flat prisms or rhomboidal crystals. EA'aporated quiet- ly, large darkly striped bodies like rock crystal are formed, besides smaller cucumber-shaped crystals. The chlorate crystallizes partly in bunches of four-sided bent prisms with curved surfaces, and partly in coarser, irregular, and darker prisms, grouped in pairs (Lehmann). It has been found in human blood in the disease knoAvn as leucaemia, (Scherer) ; in the blood of the ox and horse; in muscle, in the heart, in the liver, spleen, thymus, and thyroid glands (Scherer, Strecker, Gorup-Bes- anez), and, finally, in the kidney and urine. Xanthin, C5II4N403. Xanthin, which differs from hypo- xanthin in having one more, and from uric acid one less, atom of oxygen, forms a salt Avith nitric acid, Avbich crystallizes in bunches of rhombic tables and prisms. Chlorate of xanthin oc- curs in glittering, six-sided tables (fig. 24). Xanthin was formerly only knoAvn as a constituent of very rare urinary Fig. 23.- -Crystals of nitrate of sarkin (upper half), and of chlorate (lower half). Fig. 24.—Crystals of nitrate of xanthin (above), and chlorate (below). 44 MANUAL OF HISTOLOGY. Fig. 25.—Crystals of allnntoin. calculi; it has, however, been since found to occur very extensively, hut in small quantities, in many different organs-in the brain, in glands and muscles, and in the urine. AUantoin, C4H6N403. This compound crystallises in glittering, colourless prisms of rhombic fundamental form (fig. 25). It is difficult of solution in cold, but more soluble in warm water; not at all so in ether, on the contrary. AUantoin appear neutral, but combines with metallic oxides. Through the agency of yeast-cells it may be split up into ammoniacal salts and urea. AUantoin may be obtained with urea artificially on the oxidation of uric acid, by boiling Avith super- oxide of lead. It is a constituent of the allan- toid fluid of the embryo, and the urine of young calves. According to Frerichs and Staedeler, it ap- pears in the urine of mammals, coincident Avith disturbance of their respiratory functions, but whether in man under similar circumstances has not yet been decided. It must be regarded, like the bases with which it is physiologically related, as a decomposition product of azotised substances in the body. §30. Kreatin, C4H9N30„ + H20. This compound, knoAvn even before its constitution was accurately ascertained by Liebig, is of neutral reaction. > It is soluble, in a minor degree, in cold, more so in hot water, and quite insoluble in pure alcohol and ether. It crystallizes in transparent rhombic prisms (fig. 26), loses its water of crystallization at 100° C, and at a higher temperature melts with decomposi- tion. With acids kreatin forms salts of acid reaction. Some of the decomposition products of kreatin are also of importance. Dissolved in acid and heated, it is transformed, with the loss of one molecule of Avater, into a closely- related substance, Avhich also occurs naturally in the body; this is knoAvn as kreatinin, C4H7N30. Boiled with baryta Avater, kreatin passes into urea, CH4N20 (taking up a mole- cule of Avater), and another base, not yet met with naturally, knoAvn as sarkosin (methylglycocoll), C.2H4(CH:!)isr02. Kreatin springs, according to Volkard, from sarkosin and cyanamid = c,HAN {^ + *c*H.-ce,oiN{^H)NHi_ This is looked upon as methyhiramido-acetic acid (methyl"uanidin- acetic acid). ° Fig. 26.—Crystals of kreatin. ELEMENTS OF COMPOSITION. 45 Kreatin is found (but only in small amount) in the juices of the muscles of man, and the vertebrates generally; also in the fluid saturating the brain (in the dog, according to Staedeler, together Avith urea), in the testes (?), and in the blood (Verdeil and Marcet Voigt). In the urine it is said by Heinz not to exist primardy, but to be formed secondarily from kreatinin. Kreatin may be looked upon as a decomposition product of muscle and the substance of the brain, leaving the body through the kidneys. Per- haps the greater part of the kreatin Avhich is formed in the body under- goes immediate decomposition, and is one of the sources of urea. This seems probable Avhen we remember the mode in Avhich it is split up by boding Avith baryta water. Kreatinin, C4H7N30. This substance, nearly allied to kreatin, crystallizes in colourless oblique rhombic pillars belonging to the monoklinic system (fig. 27). In contra- distinction to the compound last men- tioned, kreatinin possesses strongly basic properties, and is readily soluble in water. With acids it combines to form crystal- line and usually soluble salts. Kreatinin may be obtained by treat- ing kreatin Avith acids. A Avatery solu- tion of kreatinin, on the contrary, be- comes again transformed into kreatin. Boiled Avith baryta Avater, it splits up into ammonia and methylhydantoin, C4H0N2O2. It is now looked upon as glykolylmethylguanidin. Kreatinin is a constituent of the juices of muscle, and appears in the urine; here it is present in large quantities, and becomes transformed, as already remarked, into kreatin. Verdeil and Marcet state that they have found it, like the latter, in the blood. Fig. 27.—Crystals of kreatinin. §31. Leucin, CeHu(NH2)02. Leucin, or amidocapronic acid, is produced by the artificial decomposi- tion of the protein compounds, glutin-yielding matters and elastin, by means of acids or alkalies. It is, likeAvise, met Avith as a product of the putrefaction of albuminous substances, like tyrosin, to be alluded to pre- sently, and as such it Avas discovered many years ago by Proust. Through the investigations of Frerichs and Staedeler, who showed it to be a physiological decomposition product Avidely distributed throughout the body, it has become of much interest. Contributions on the same point have also been made by Cloetta and Virchow. Many of these statements, moreover, are confirmed by Gorup-Besanez and Radziejewsky. Leucin is met with as a crystalline substance, partly (but only rarely and when very pure) in delicate klinorhombic plates, partly in spheroidal lumps possessing a very characteristic appearance. They are either small globules (a), or hemispheres (b b), or aggregations of rounded masses (c c d), 46 MANUAL OF HISTOLOGY. and not rarely a number of segments of small spheres rest with their flat side upon a larger globe (d ef). Leucin globules may be either unmarked (in Avhich ease they slightly resemble fat-globules), or they may present a concentrically laminated appearance (g g g g). They are frequently met with also with rough surfaces, as though eroded.- Leucin has no action upon vegetable colours, is quite soluble in water, hydrochloric acid, and alkalies, and slightly so in cold alcohol, while in ether it is insoluble. It may be volatilised by a cautious elevation of temperature. Bapidly heated, it fuses with decomposition. From its solutions it is not precipitated by most of the usual reagents. In regard to the occurrence and significance of this substance in the human system, we must distinguish between leucin produced by the putrefaction of histogenic substances, and that formed physiologically in the living body. The latter appears often, but not invariably, accompanied by tyrosin as a constituent of many organic fluids and gland juices, in greater or less quantity, Under diseased conditions it is often unusually abundant in organs in Avhich traces alone are to be found during health, as for instance in the liver. It is present in the spleen, the pancreas, and its secre- tions, the saliArary glands and saliva; in the lymphatic glands, the thymus and thyroid glands, and in the fluid saturating pulmonary tissue. In the healthy liver it is not to he found, or only so in traces, as is also the case with the brain. Muscle appears like- wise to be destitute of leucin, though in the heart it may not unfrequently be found as a pathological product. It is at times present in large amount in the kidneys, and may pass Fig. 28.—Spheroidal crystalline masses of leucin. a, a very minute simple spherule; b. hemispheroidal masses; c c aggregates of small globules; d, a large globule sup- porting two halves; e /, a large spheroid of leucin richly studded with minute segments; g g g g, lamin- ated globules of leucin, some with smooth, some with rough surface, and of very various sizes. rp, - , , . into tne urine (Staedeler). Ihese facts are of some physiological worth, in that thev prove the existence m different organs of distinct series of mutations anion" their histogenic substances. Ihus, leucin is no mutation product of muscle but of many glandular structures. There can be no doubt, further that as artificially, so also m the system naturally, does leucin sprinc/from protein compounds, gelatin-yielding substances and elastin; its Jhvsio logical origin from albuminates by the action of one of the femiente existing in the pancreatic juice has also been proved (Kiihne). LeUcill 'H nnrfiallv ovnraforl ttt.'^V. 4-1, - —1-_ 11 * '* appears ion partially excreted with the glandular secretions, and a in the intestinal canal, and probably undergoes further decomposit also in the body It is a fact Avorthy of notice, that in the lymphatic and blood-vascular glands, there occurs besides leucin amm™,*, {i ii • of the hypothesis that leuciu maJ he resold™ a^S ELEMENTS OF COMPOSITION. 47 volatile fatty acids (Frerichs and Staedeler)—a change which certainly takes place in the loAver part of the intestinal canal. §32. Tyrosin, C8HnN03. This substance is also an amido-acid, whose constitution, however, has not yet been fully ascertained. It possesses Aveak basic properties, and may be obtained like the foregoing, but in much smaller amount, from the artificial decomposition of protein matters. Not, hoAvever, like leucin, from that of elastin and gelatin-yielding substances. It is also produced by the putrefaction of protein compounds, and in. especially large quan- tity from the decomposition of silk-fibrin and glue. Keratin and animal mucus also yield more tyrosin by far in their decomposition than the original protein matters. Thus we see it to be associated chemically with leucin, and it has been recently proved to be a physiological companion of the same as a constituent both of the normal and diseased body (Frerichs and Staedeler). Tyrosin, nevertheless, is not so extensively met Avith as leucin. It crystallizes in white silky needles (fig. 29, a) Avhich are frequently arranged in very delicate, small, or large groups (b b). While leucin is very soluble in water, tyrosin is but little so, besides 'which it is insoluble in the pure state in alcohol and ether. It fuses with decomposition Avhen heated, and combines in regular propor- tions with acids and bases. Warmed with concentrated sulphuric acid, there is found in it, beside other acids, a compound named tyrosin-sulphuric acid, which, like its salts, when mixed Avith chloride of iron assumes a beautiful violet colour (Piria's test). This reaction with chloride of iron just mentioned resembles that of the salicylecompounds, although its nature has not yet been as- certained. Without taking into account the tyrosin developed in the processes of putrefaction in the body, Ave find that it has similar physiological sources to the fore- going base. It is missed in the healthy liver like leucin, pro- bably because it undergoes there rapid transformation into other compounds. In disease, hoAv- ever, it appears in this organ. Tyrosin Avhich, as has been already mentioned, springs in smaller quantities from albu- minous substances than leucin, and lacks besides the physiologi- cal sources of the latter from gelatin and elastin, as well as its solubility, is frequently missed where leucin occurs. Thus it has been found alone Fig. 29.—Acicular crystals of tyrosin. a, single crystals b b, smaller and larger groups of the same. in no inconsiderable amount in the 48 MANUAL OF HISTOLOGY. spleen and tissue of the pancreas, as also in the digest of albumen in pancreatic juice. The physiological significance of tyrosin is probably in general allied to that of leucin. §33. Glycin, C2H3(NH2)02. Glycin or glycocoll, or also glutin sugar, which is in reality amido-acetic acid, has not as yet been met Avith free in the system. It appears, how- ever, on the splitting up of several animal acids, as hippuric and uric, and one of the biliary acids, namely glycocholic. It is also of interest as an artificial decomposition product of glutin and chondrin. It is obtained in greatest abundance by the decomposition of silk-fibrin (fibroin), in Avhich it is present together Avith leucin and tyrosin. It may be artificially produced from chloracetic acid by the action of ammonia. Glycin crystallizes in colourless rhombic pillars belonging to the mono- klinometric system (fig. 30). These crystals bear a heat of 100° C. Avith- out losing any water, but at 178° C. they fuse, and are decomposed. Glycin is sweet to the taste, without alkaline reaction, soluble in Avater, but almost insoluble in alcohol and ether. It forms acid salts Avith acids, and can combine with bases or even salts themselves. There 0\v \J> must be some substance nearly related to glycin \ f\ \\ formecl in tne hody, in all probability from ( \ \\ \\ Smtinous matters (although at present we are unacquainted with it), Avhich in combination with cholic acid constitutes glycocholic acid, and Avith benzoic, hippuric acid. This sub- stance then becomes free in the form of glycin upon the absorption of Avater, and splitting up of the two acids. Glycin leaves the body partly Avith hippuric Fig. 30.—Crvstais of civcin 0f ' a(dd through the kidneys, and is partly reab- different form,. sorbed into the blood as a component of glyco- cholic acid as (shown by Bidder and Schmidt) in order to undergo there further alterations Avith Avhich Ave are unacquainted. Cholin, Neurin, C5H15N02, or C2H4 j gH, ^ Some years ago a neAv base knoAvn as cholin Avas met with by Strecker (in but small quantities, however) in the bile of oxen and swine We know that by boiling lecithin with baryta water neurin is obtained (S 20) a base of strong alkaline feaction. The identity of this substance with chohn has recently been established in a very interesting way Neurin is now regarded as hydrated oxide of trimethyl-oxethyl-ammonium (Baener) Finally, Wurtz succeeded in producing hydrochlorate of neurin from hydrochlorate of glycol and trimethylamin. §34. Taurin, C2H7NS03, or C2H4 j ^ This substance, containing as much as 257 per cent, of sulphur Avas ELEMENTS OF COMPOSITION. 49 Fig. 31.—Crystals of tanrin. a, well-formed six-sided pri>ms; 6, irregular sheaf-like masses from an im- pure solution. artificially. OH SO.H. It is related to discovered long ago as a constituent of the bile. It crystallizes with the fundamental form of a right rhombic prism (Avhose lateral angles are respectively 111° and 68° 16'), in colourless six-sided prisms, with four and six facets on their extre- mities (fig. 31, a). From im- pure solutions it separates in irregular sheaf-like masses (6). Taurin has no effect upon vegetable colours; it is toler- ably soluble in Avater, but insol- uble in alcohol and ether. The great stability of the substance is remarkable: even boiling in mineral acids in which it dis- solves does not decompose it. Taurin is not precipitated from its solutions by tannic acid and the metallic salts. The sulphur it contains Avas for a long time overlooked ; it is contained in it in a different combination to that which exists in cystin. Taurin has recently been produced isethionic or sulfethylenic acid, C2H4< Isethionate of ammonium, when heated up to 200° C, according to Strecker, yields taurin, Avith the loss of one molecule of water. c.H.{s0oVrH'0=c'MsoHk. Thus taurin is an amido-sulfethylenic acid. Kolbe obtained it also by the action of ammonia upon chlorethyl- sulphuric acid. Taurin may be obtained by the splitting up of one of the two biliary acids, and contains all the sulphur of the bile. It also becomes free on the decomposition (commencing in the body) of this acid knoAvn as taurocholic, and appears thus in abnormal as Avell as putrid bde, and in the lower portion of the intestinal canal (Frerichs). It has been also met Avith by Cloetta in the juices of renal and pulmonary tissue. As obtained from the latter source, it Avas formerly described by Verdeil as pulmonic acid. The suprarenal capsule contains it also (Holm), though the blood does not. At present Ave are uncertain as to the origin of -taurin; but it has all the nature of a decomposition product, and there can be hardly any doubt (from the fact of its containing sulphur) that it is derived from albuminous matters, a considerable quantity of the sulphur of the latter being present in it. In regard to its farther changes, an observation has been made by Buchner of great physiological interest. Taurin, othenvise so stable, splits up by the action of a ferment (namely, the mucus of the gall-bladder) in the presence of alkalies, into carbonate of ammonium, sulphurous, and acetic acids. The latter acid, combined with an alkali, is changed into a carbonate, and the sulphurous acid in combination with sodium becomes later converted by oxidation into sulphuric acid, so that in 50 MANUAL OF HISTOLOGY. putrefying bile we meet with Na.2S04. The circumstance that most of the bile poured out into the intestine is reabsorbed as observed by Bidder and Schmidt, thus explains, at least partially, the origin ot the sulphates, which eventually leave the body Avith the urine. Cystin, C3H7NS02. This substance is remarkable for the large quantity of sulphur which it contains, amounting to over 26-5 per cent. _ Cystin crystallizes in colourless hexagonal tables Of) or prisms (fig. 32), and is insoluble in Avater, 1 alcohol, and carbonate of ammonium. It is, on If the other hand, readily soluble in mineral acids Q ~. and in alkalies, from which it may be precipitated I ^~> by organic acids, as, for instance, by acetic acid. C\ C3 ^Taa Cystin enters into combination Avith both acids ^-^ ^^^ \LZ_1 an-d allies. Its mutation products and consti- ^^r tution have not as yet been ascertained, nor do 32.-Crystais of cystin. we knQW {n what form suiphur is contained in it. Cystin is of rare occurrence; it forms certain kinds of urinary calculi, and may also appear as an abnormal constituent of urine. It Avas once met Avith in the liver (Scherer); likewise in the tissue of the kidneys of oxen by Cloetta, but not invariably. The physiological relations of the substance are still quite obscure. I. Animal Colouring-Matters. §35. The animal colouring-matters, Avhich are not found in the vegetable kingdom, have their origin for the most part1 from the natural pigment of the blood, haemoglobin (§ 13). They are met Avith either as artificial decomposition products, or occur in the living body. Haematin, C34H34NT4Fe05 (Hoppe). This substance, as already mentioned, may be obtained from the red blood-corpuscles or haemoglobulin, hut only in a coagulated form. According to Hoppe, haematin usually presents itself as an amorphous blue-black substance, which becomes of a reddish-broAvn on being triturated. It is insoluble in Avater and alcohol, but soluble in the latter if there he added to it a certain small amount of sulphuric or nitric acid. It may likeAvise be dissolved in a watery or spirituous solution of ammonia ; and also in caustic alkalies in dilute watery or alcoholic solution. Such a fluid containing haematin is frequently changed to a greenish colour by the action of a large amount of potash—especially if it be boiled. Haematin, suspended in Avater, is decolorised by the action of chlorine Avith the formation of chloride of iron ; the dried powder also becomes green by contact Avith chlorine gas. Dichroism is seen in alkaline, but not acid solutions of haematin; in a thin layer they appear olive-^'reen in a thick stratum red (Brucke). With the aid of concentrated sulphuric acid, the iron it contains may be extracted from haematin, water taking its place in the com- bination (Hopjpe). Hydrochlorate of Haematin, Hsernin, C34H34N4Fe05. HC1 (Hoppe). We are indebted to Teichmann for our acquaintance with this peculiar ELEMENTS OF COMPOSITION. 51 Fig. 33.—Crystals of haemin. crystalline element of the blood. Dried blood, treated with Avarm acetic acid, even when putrefaction has already set in, deposits regularly innu- merable crystals of broAvn, dark-broAvn, or almost black colour, -which appear either in the form of rhombic pillars (Avhen they resemble haematoidm), or in needles, single or arranged in stellate groups (fig. 33.) The presence of chlorides of the alkalies is, as Teichmann very properly remarks, indispensable for the occurrence of this crystallization. Haemin crystals are tolerably stable, do not decompose in the air, and are neither soluble in water, alcohol, ether, nor in acetic acid. They may be dissolved, however, in boiling nitric acid. Sulphuric acid likewise reduces them readily to solution, as also ammonia and Aveak potash. The latter, Avhen concentrated, changes the colour of haemin crystals to black, causing them at the same time to swell up. These crystals are of the greatest importance in a forensic point of view, as a means of proving the presence of small quantities of blood. Kuhne obtained them from the colouring matter of muscle. Until a few years ago, the chemical constitution of haemin was but very imperfectly known. We are indebted to Hoppe for the first accu- rate inAestigations of the subject. By him it was produced from pure haemoglobin (see above), besides which he demonstrated that it might be again reconverted into ordinary haematin. Haematoidin, C17H18N203, or C34H36N'406 (?) Blood Avhich has left the vessels, and is stagnating in the tissues, undergoes gradually farther changes, by Avhich a crystalline colour- ing-matter is formed, nearly allied to hamatin, but destitute of iron. This, Avhich is knoAvn as haematoidin, crys- tallizes in rhombic prisms (fig. 3f), but also in acicular crystals (Robin). Under the microscope these appear red Avith trans- mitted light; with reflected, of a canthara- dine green colour. Haematoidin is very soluble in chloroform, to which it communi- cates a golden yelloAV tint, and also in sul- phide of carbon, Avhich acquires from its presence a flame colour. Its crystals are likeAvise dissolved by absolute ether, but not by either absolute alcohol, Avater, ammonia, solution of soda, or ddute acetic acid : in concentrated acetic acid, however, they dis- solve Avhen Avarmed, communicating to the fluid a golden-yellow colour (Holm). Staedeler obtained unusually large crystals of this pigment, measuring as much as 0'45mm. from the ovary of the cow, by treatment with chloro- form or sulphide of carbon (fig. 35). They appear under the micro- scope, in the first place, in the form of acute-angled triangular tables Avith one convex side, a. This cunred border, hoAvever, may be replaced by Fig. 34.—Haematoidin crystals. 52 MANUAL OF HISTOLOGY. two Fig. 35 from ment rWit lines, giving rise to deltoid tables (6). Again, two such tables very frequently become fused together by their convex sides, or overlap each other (be). We then have ' the rhombic tables usually ascribed to haematoidin (fig. 34) ; still shoAving indentations in most cases at the blunt angle of the rhombs, Avhich gradually become obliterated (dd). It not unfrequently happens that tAvo other crystals become asso- ciated Avith the tAvo first, so that a four-rayed star is produced (e). These then give origin to four-sided tables on the filling up of the indentations at their corners, and each sometimes , « u » -,,• assumes eventually the appearance of -Very large crystals of hsematoidin «•*""'«"> j rr . - an oblique dice, from its having gradually become thickened (fg.) the ovary of a cow, obtained by treat- an oblique with chloroform §36. Uroerythxin, or Urohaematin. In the urine a very small quantity of a red colouring matter is to be found, Avhich gives to the fluid its yellow tint, and may colour the sediment of the same of a lively red. This substance is very unstable, and only obtainable with great difficulty, whence our imperfect acquaint- ance Avith its nature. The colouring matters of urine Avere first investigated by Scherer, and more recently by Harley. The latter obtained a red pigment almost insoluble in water, but freely so in Avarm fresh urine, giving to the latter a yellow tint, and to ether and alcohol, in which it is also dissolved, a beauteous red colour. Harley found this pigment to be ferruginous, and regards it as a species of modified haematin. Besides this, some other pigmentary matters were also met Avith by him. A red pigment has been recently discovered by Jaffe in the urine, possessed of some spectroscopic peculiarities : it has been named by him urobilin, from the fact of its also occurring in bile and the excrements. Blue and violet colouring matters, which may occasionally be met with in human urine, appear in but very small quantity. Under certain circumstances indigo has been observed here without having been taken up from without (Sicherer), while indikan, C26H31]Sr017, or chromogen of indigo is, according to Hoppe, constantly present. Black Pigment, or Melanin. Black pigment is found in normal tissues in the form of very minute granules or molecules. It is a substance remarkable for its insolubility and unchangeableness. Melanin is not soluble either in Avater, alcohol ether, dilute mineral acids, or concentrated acetic acid. It is dissolved in warm potash solutions, but only after some considerable time The same takes place in concentrated nitric acid, by which the melanin is decom- pounded, however. Its ash contains iron. The investigations in regard to the constitution of melanin which have ELEMENTS OF COMPOSITION. 53 hitherto been made, must be received with reserve, for the substance is only to be obtained pure with the greatest difficulty. Melanin, Avhich Avith haematin is the only pigment in the body to which a certain amount of histogenic significance cannot be denied, appears, as a rule, forming the contents of polygonal or stellate cells. It is met Avith in greatest abundance in the interior of the eye. The large amount also in which it is met Avith in some of the lower vertebrate animals, as for instance in the frog, is remarkable. As a pathological product, it (or something nearly allied to it) is frequently met with in great abundance in different organs, tumours, &c. The source of melanin is usually, and probably correctly, supposed to be the colouring matter of the blood. This view is borne out by the nature of pathological black pigments, Avhose origin from haematin may in many cases be accurately traced. We must be on our guard, however, not to confound the ordinary black pigment found in the human lungs with melanin. This consists of particles of carbon, charcoal, dust, or lamp-black, suspended in the air Avhich is inspired. It is not met with in the lungs of infants or of wild mammalian animals. §37. Biliary Pigments. Until very recently but little has been known of the colouring matter of the bile. It is characterised by its reactions with nitric acid. The latter, if it contain nitrous acid, or if concentrated sulphuric acid be added to it, produces in bile a peculiar play of colours,—green, blue, violet, red, yellow, following rapidly one upon the other. Two kinds of pigment may be usually distinguished in bile : a brown, known as cholepyrrhin or biliphaiin, and a green or biliverdin. According to Staedeler's recent investigations, a whole series of probably characteristic pigments may be obtained from bile, although it is still a question Avhether they all exist in the latter when perfectly fresh. Bilirubin, C16H18N|0, (or C9H9X02?) A red substance allied to haematin and haematoidin (but not identical Avith the latter), which may be obtained from its solutions in chloro- form, sulphide of carbon, and benzol, in beautiful ruby-red crystals. These (fig. 36), when crystal- lized from sulphide of carbon, appear in clino- rhombic prisms, Avith a basal surface, whose foremost angle is very sharply curved, and prism surface convex, so that a view of the basal surface presents an elliptical figure. Lying upon their convex surface these crystals have a rhombic form. Bilirubin is insoluble in water, and nearly so in ether. It is soluble, on the other hand, in alkalies and in chloroform, communicating to the latter a pure yelloAV or orange-red colour; also in sulphide of carbon, which is tinged golden yellow by it. It possesses, further, the properties of a Aveak acid, and shows the play of colours just mentioned with nitric acid containing nitrous acid in the most Fig. 36.—Crystals of bilirurbin separated from sulphide of car- bon. 54 MANUAL OF HISTOLOGY. marked degree. It is the most essential colouring matter of human bile and biliary calculi, and is probably derived from haematin; it is also found in the urine of persons suffering from jaundice (Schwanda). Biliverdin, C16H20¥2O5, or (CbH9N02?) This is a green colouring matter, which may, under certain circumstances, be obtained in a crystalline form. Its presence in fresh bile is still questionable, for it is probable that it absorbs water and passes into biliprasin, a coloring matter, to be presently alluded to. The relation- ship to bilirubin will be easily understood from the following formula :— C16H18N203 + H,0 + 0 = C16H20N2O5 Bilirubin. Biliverdin. Bilifuscin, C16H2JIsT204. A non-crystallizable compound, soluble in water, containing soda or ammonia, communicating to it a brown colour. It is, to all appearances, of subordinate importance, and differs from bilirubin only in having one more molecule of H,0 . Biliprasin, C16H22lSr206. A green amorphous pigment, soluble in alkalies with a brown colour, in contradistinction to biliverdin, which, Avith the former, produces a green solution. The formula of this pigment corresponds to that of biliverdin + one molecule of H20. It occurs in biliary calculi and jaundiced urine. Bilihdmin, finally, is a name given by Staedeler to a dark earthy-looking substance, Avhich, however, has not yet been obtained perfectly pure, so that its formula is not known. It may be obtained as the ultimate decomposition product of all the four biliary pigments like melanin. Remarks.—It may be well at this juncture to bestow a few words upon the extractive matters. Under this name we understand in zoochemistry, a set of sub- stances which are partly present in the body naturally, and are partly the results of chemical manipulation. They manifest no characteristic peculiarities by which they may be recognised ; they do not crystallize, nor combine in regular proportions with other matters, nor do they volatilise at definite temperatures. From this may be perceived the difficulty of dealing with these substances, either chemically or physio- logically. Our chemical acquaintance with them is therefore very incomplete. Physiologically they are held to be decomposed materials, intermediate products in mutative processes, although in reality there is but little proof that this is the case. Several bases, acids, &c, already alluded to, have recently been separated from these compounds. K. Cyanogen Compounds, §38. As a supplement to the consideration of the azotised decomposition products of the system, cyanogen, CN, and its combinations may be appended here. Sulphocyanogen (rhodan), CNS. This ternary radical, whose com- pounds are remarkable for the beautiful red colour which they produce with salts of iron, forms with H what is known as hydrosulphocyanic acid H | S. Unlike other compounds of cyanogen, this is generated in the human body, and possesses but slight poisonous properties. It occurs in combination with potassium. ELEM ENTS OF COMPOSITION. 55 Sulphocyanide of potassium (rhodanide of potassium), -^ > S , is the only cyanogen compound met Avith in the human economy, and that in extremely small quantity. It is a constituent of saliva, in which it was discovered by Treviranus; its occurrence here, however, is not without exception. The origin and relations of this compound are still entirely unknown. Sulphocyanide of potassium gains in interest, moreover, Avhen Ave remem- ber that in the physiological mutation series no other cyanogen combina- tions make their appearance. L. Mineral Constituents. §39. The number of mineral substances and inorganic compounds occurring in the human body is not inconsiderable. Our knowledge of these, how- ever, is unfortunately far less perfect at present than the nature of the substances in question might lead us to expect. In respect to the com- bination of inorganic matters, we are—so far as the question turns upon their pre-existence in the various parts of the body, or to Avhat extent they must he regarded as only produced by chemical manipulation itself —by no means as clear as might be desired. But greater obscurity still prevails in regard to the physiological relations of some of these substances. a Granting, for instance, that no doubt can exist that in Avater we have before us the chief solvent and agent in saturation and gelatinization of the system, and that phosphate of calcium constitutes the most important hardening medium of the same, and so on, there remains still a consider- able number of substances whose purposes in the body we are unable to ascertain Avith anything like certainty. It is likewise beyond our power at present to distinguish Avith precision between those inorganic com- pounds which occur as decomposition products in the economy, and those which possess histogenic properties. Finally, there are in all probability many mineral matters in the system Avhich are only casual constituents of the same, introduced with the food. It would lead us too far to detail here all the differences in amount between the ash constituents of the several tissues and organs of the body. The variation in this respect, according to age, is of such great interest, hoAvever, that a feAv points may be noticed in regard to it. While, in the earlier periods of foetal life, the ash only amounts to 1 per cent, of the Avhole weight of the body, it rises later on to 2, and reaches in mature mammals so high as 3*5, 4, or even 7 per cent. In advanced age it is probable that this is still further increased (Bezold and Schlossberger). Among the inorganic matters and compounds found in the body, the folloAving must be specially borne in mind :— (a.) Gases—oxygen, nitrogen, and carbonic acid. (b.) Acids—carbonic, phosphoric, sulphuric, hydrochloric, hydrofluoric, and silicic. These, Avith the exception of the carbonic acid, diffused through fluids, and hydrochloric acid, found free as a constituent of the gastric juice, hardly ever occur in a free state in the body, but almost invariably combined Avith bases. (c.) Bases—potash, soda ammonia, lime, magnesia, oxides of iron, man- ganese (and copper). These usually appear as salts, and yet Ave have free 56 MANUAL OF HISTOLOGY. alkalies, especially soda, combined with protein compounds, and also iron, in many animal substances, as, for instance, in haemoglobulm and me- lanin. . . , In regard to the gases just mentioned, they are found either in the cavi- ties of the body, or diffused, or chemically combined in its various fluids. Oxygen, 0. Oxygen occurs in the organic matters of the animal body in combina- tion. It appears, hoAvever, also as an element in all the air cavities of the system. Finally, it is met Avith in all the fluids of the economy. In the blood oxygen is dissolved in very minute quantity, Avhile the greater por- tion appears combined (though loosely) with the other constituents of the fluid. AVe need hardly remark that this element, from its strong tendency to combine with other substances, plays a most important part in the chemical and physiological life of the organism. Nitrogen Gas, N2. Nitrogen, as is Avell known, occurs in combination in many organic matters in the body: it is also met Avith, however, in the air cavities of the latter, and in very small quantities dissolved in its various fluids. Carbonic Acid, or Carbonic Dioxide, C02. Carbonic acid appears partly in combination (especially with inorganic bases), partly free, either as a gas, or dissolved in the fluids of the body. As a gas, carbonic acid is present in considerable quantity in the gases expired from the lungs, and in various cavities containing air. Dissolved, it is a constituent (though in variable amount) of all animal fluids. It appears in abundance in the blood, moreover, partly free and partly com- bined. Carbonic acid, which is introduced into the economy in hut small amount from without, is the most important end-product of many chemical mutation series in the body. It leaves the latter in large quantities through the lungs, and to a small extent with the exhalations of the skin. §40. Water, H20. No inorganic compound is of such great importance for the existence of the organism, or occurs throughout all its parts in such abundance as water : without it life is impossible. Setting aside that which occurs' in hydrates and in crystals, water is necessary to the organism, in the first place, as a solvent for many of its constituents. By virtue of this property it renders an interchange of material possible. Dissolved in water the alimentary matters are absorbed into blood and tissues, and by it effete substances are carried out of the body. In the preceding section we have already alluded to its power of absorbing gases. The proportion of water to the whole weight of the body is in General very considerable; in the higher animals at a period of maturity it is on an average, about 70 per cent., while in embryos it is still larger ranaino- from 87 to 90 per cent. In the infant and in younger animaTslts amoZ gradually sinks, while that of solid organic and" mineral mattesund™ oe constant increase (Schlossberger, Bezold). That the proportion of X in different parts of the body varies to an enormous extent is quite evident" ELEMENTS OF COMPOSITION. 57 and Avill be alluded to later on more in detail. For the present it need only be remarked that, as Avater, on the one hand, renders possible all the chemical occurrences of the body by virtue of its solvent power, so, on the other hand, does it communicate to each tissue its individual stamp, from a physical or physiological point of vieAv, as an imbibed mat- ter. Its amount in the soft, semi-solid portions of our body appears dis- proportionally large, but eA-en in the harder structures, such as bone, it is not inconsiderable. Besides that Avhich is generated Avithin the body by oxydation from the H of organic substances, water is introduced into the body with food, both solid and liquid. Hydrochloric Acid, C1H. This acid is only found free in the gastric juice. Silicic Acid or Silicon Dioxide, SiOa. Very small quantities of silicic acid, either free or combined in salts, have been met with in human blood (Millon), saliva, urine, bile, and excrement, as Avell as in biliary and urinary calculi, bones, and teeth. But of all the tissues of the human body, the hairs, according to Gorup- Besanez, contain most of it. Silicic acid is taken into the body with the food and drinking water, and passes out of the same, for the most part, immediately through the intestinal canal, while a portion of it is absorbed into the blood, and appears later in the secretions of the various glands. The physiological or anatomical significance of silica in the human system is not knoAvn. §41. Calcium Compounds. Lime, CaO, which next to soda is the most important inorganic base of the body, presents itself in many different combinations. Phosphate of Calcium. Phosphoric acid occurs, as is Avell known, under various modifications, of Avhich, hoAvever, only the ordinary or tribasic acid appears in the system. The folloAving are its calcium salts : (a), Acid phosphate of calcium, as it is called, CaH4P208; (b), Neutral phosphate, CaHP04; and (c), Basic phosphate, Ca:1P208. Basic, Ca3P2Oh, and neutral CaHP04, phosphates of calcium. The first of these is almost insoluble in water, but to a certain extent soluble in that containing carbonic or organic acids, as also in solutions of ammonium salts, chloride of sodium, and of animal gelatin. It is, as we have seen, the particular salt of calcium which occurs in the bones and teeth, and probably exists besides widely distributed throughout the animal body, Avhile the acid salt is present in human urine. Phosphate of calcium, Avhich has its origin in general from the alimentary matters, appears in very variable amount in all the solid and fluid portions of the system. AVherever it is present in large quantities it is the most important hardening agent of the latter. Its deposits are almost always amorphous. Phosphate of calcium has been shown to exist in the blood, urine, gastric 58 MANUAL OF HISTOLOGY. juice, saliva, semen, and milk, as well as in the juices of organs. Again, it invariably accompanies histogenic substances, as has been already men- tioned, and appears with the same in the tissues and fluids of our body. It is present in bone in large quantities as the chief constituent of the hard material of this tissue known as bone earth. But in the enamel of the teeth, the hardest substance in the whole body, it exists in still greater quantity. Phosphate of calcium must he regarded as an indispensable element of the tissues of the body ; we must, therefore, ascribe to it histogenic properties. Carbonate of Calcium, CaC03. This, like the preceding salt, occurs in the amorphous condition as hardening material in bones and teeth, but only in small amount. Be- sides this, it is met with in some of the animal fluids, as, for instance, the saliva, and in alkaline urine. It is also found in a crystalline form in the internal ear of man, constituting Avhat are known as otoliths. It is met Avith more frequently still, however, in this state, in the bodies of the lower vertebrates, as, for instance, in frogs, deposited upon the mem- branes of the brain and spinal cord, and also on the anterior aspect of the spinal column, about the place of exit of the spinal nerves. Otoliths (fig. 37) are small crystals of short, thick, columnar form, com- binations of rhombohedrons and hexagonal prisms in their fundamental figure; among them may also be found pure rhombohedrons, or scaleno- hedrons. The question as to Avhat it is that retains carbonate of calcium in solution in the fluids of the body, has not yet been answered satisfactorily. It seems probable, hoAvever, that the carbonic acid diffused through the latter is the real solvent for the salt. Any other physiological purpose besides that of a hardening medium of the second class, has not as yet been recognised for carbonate of calcium as it appears in the bodies of the higher animals. Carbonate of calcium is partly taken up as such from without, and is partly O ft A^!3 ^ formed in the body by the develop- €IA/? z^7^ 5£§ ment of carbonic acid as a decom- ^SJjJfcP Q ^W^ position product (see above). % \^ Chlorioe of Calcium, CaCl2. Fig.ST-Otolithsconsistingofcarbonateofcalcium J* ?f ^ Sub°rdinate significance, ., . . . . , , D • and has as yet been met with in the gastric juice only (Braconnot). Fluoride of Calcium, CaFI2. This salt is found in the enamel of the teeth and in small quantities in bone also; traces of it are also met with in the blood, milk, and urine saliva, and bile, and in the hairs (Nickles). Fluoride of calcium S taken up from without as such. ; -nuonae oi calcium is §42. Magnesium Compounds. Magnesium appears under similar circumstances, combined with phos- ELEMENTS OF COMPOSITION. 59 phoric acid, like calcium, mentioned in the preceding section. Its amount, however, is everyAvhere smaller than that of calcium. Phosphate of Magnesium, Mg3P2Og + 5H20, or MgHP04 + 7H20 . We are not yet able to state Avhich of these two salts it is Avhich occurs in the body.—Like phosphate of calcium, the corresponding combination of magnesium is met with in all the fluids and solid portions of the body.—It is one of the hardening constituents of bones and the teeth, but only in a minor degree. The preponderance of phosphate of magnesium over the corresponding salt of calcium in muscle and the thymus gland (Liebig) is of interest. It is taken up as such from Avithout, and is offered to the body in superabundance by a vegetable diet, so that the greater part of all that is received into the body passes through the intestinal canal unabsorbed. Phosphate of Magnesium and Ammonium, MgNH4P04 + 6H20. During putrefactive decomposition, or indeed Avith every generation of ammonia in the system, the latter combines with phosphate of mag- nesium to form a crystalline salt known as phosphate of magnesium and ammonium. This salt (fig. 38) is found in crystals of rhomboid funda- mental form, and appears most generally in three sided prisms bevelled at both ends on one of their edges; this form is knoAvn as the "coffin-lid crystal." Further varieties are produced by the bevelling of tAvo polar opposed angles, or finally of the tAvo remaining ones. Crystals Of phosphate Of magnesium and 1"'K- 38.—Crystals of phosphate of mag- J . , i /• i ■ i- i ll nesium and ammonium. ammonium are to be found in faecal matter, alkaline urine, and all putrefying animal substances. Carbonate of Magnesium Is of very minor importance in animal life. It is met with in the urine 2CO 1 of the vegetable feeders, probably as a bicarbonate ,, „ > 04 also, per- haps, in bones. It is very difficult, namely, to determine whether it is the carbonate or phosphate of magnesium that exists in the latter, however. Chloride of Magnesium, MgCl2. This salt is said to be present in the gastric juice. §43. Sodium Compounds. While the lime compounds appear, as a class, to possess in part the characters of hardening materials for the animal body, those of soda seem entirely devoid of these qualities as far as Ave knoAv. On the other hand, however, they appear to play an important part in the chemical occur- rences of the economy, although as yet we have not arrived at satisfactory conclusions in regard to all their purposes. It has been mentioned before (pp. 15-17) that soda is combined Avith the protein substances ofthe system, and retains the latter in solution ; also that, combined with the tAvo biliary acids, it forms the most important constituents of the bile (pp. 40 and 41). 60 MANUAL OF HISTOLOGY. Chloride of Sodium, NaCl. This salt, Avhich is soluble in water, never meets with an opportunity for crystallization within the body, but may be found in crystals upon the surface of the latter under certain circumstances. These crystals (fig. 39) assume the form of dice, frequently marked Avith step-like depressions on their surfaces, or may be met Avith in the form of square prisms. Mixed Avith urea this salt crystallizes in the form of octahedrons, or, according to C. Schmidt, in tetrahedrons also. Chloride of sodium, or common salt, is to he found in all animal fluids, and in all the solid parts of the body. Its amount in the juices is variable, but seldom exceeds 0-5 per cent. The fluid Avhich saturates muscle is poorer than any in chloride of sodium. We see also, on the other hand, that though the animal juices may be at one time supplied with a larger quantity of the salt than at another, still the proportion in each fluid is tolerably constant, the surplus passing rapidly out of the body with the urine. The quantity of the substance in question is not less variable in the solid portions of the system ; the blood- cells are extremely poor, while cartilage is rich in it. An extremely interesting fact has been pointed out by Bidder and Schmidt, namely, that starving animals very soon cease to void chloride of sodium in their urine,—an indication that it is retained by the tissues and juices in the most determined manner as an indispens- 0 1M?I nm able ingredient in their composition. iB^ Jhs. mm Some of the discoveries of pathology, also, bear out this conclusion, shoAving, as they do, that during the rapid forma- tion of cells in exudations, the excretion tig. 39.—Different crystalline forms of hf ssfllt wi'fh +ho v.™'™ „l 4. i chloride 0f sodium. &au Wltn tlle urine almost ceases, and - ,..... % tnat an extraordinary amount of chloride of sodium is required for the plastic process (Heller, Redtenbacher). The ET/M° gathfed/r°m observati™ of domestic animals may a o be alluded to here In them the effect of a greater admixture of the salt m question with their food may be seen in the way it favours the whoie process of assimilation (Bousswgault). All these facts seem to point to the conclusion, that chloride of sodium must oe regarded as possessing the nature not only of an aliment hut also of a histogenic ingredient of animal tissue. But as to i ' p kno^of ttnt * "" * »» **' ™ ^ P— ** Tin* Carbonate of Sodium, Na2C03, and NaHCO ^«i anything cr^r^t^ t:rot ELEMENTS OF COMPOSITION. 61 Phosphate of Sodium, Na2HP04, and NaHJ?04. Like potassium, to be alluded to presently, sodium forms three combina- tions Avith phosphoric acid, namely, basic phosphate of sodium, Na^POj; neutral phosphate of sodium, with tAA^o atoms of base, NaJffPO.,; and an acid salt with one atom of base NaH2P04. The first of these probably does not occur in the system, so that we have only to deal with the two last. Of these the neutral salt is the most common. Phosphate of sodium is widely met with throughout the body. It has been found in the blood, the milk, the bile, the urine, and in the tissues. It is, perhaps, the baarer of the carbonic acid of respiration, and is, pro- bably, the solvent for many matters, as, for instance, casein and uric acid. It probably plays an important part, also, in the formation of tissues, which is not yet fully understood. Sulphate of Sodium, Na2S04. Like the sulphates of the alkalies generally, this salt is found in animal fluids, especially in urine, and in the excrements. In some of the most important secretions, however, it is not met Avith, as, for instance, in the gastric juice, the bile, and the milk. Like other sulphates, it cannot be said to possess any histogenic properties, but rather those of a decomposi- tion product, the sulphur of the protein compounds and allied substances, forming sulphuric acid by oxidation, and displacing the carbonic acid of the soda salt. In confirmation of what we have just stated, the facts maybe adduced— first, that sulphates introduced into the body are rapidly excreted, and on the other hand, that after an abundant fleshy diet their amount in the urine increases (Lehmann); secondly, that the sulphur of taurin, as already mentioned (see above, p. 49), is set free under the action of ferments in the form of sulphurous acid Avhich becomes subsequently con- verted into sulphuric acid by oxidation (Buchner). §44. Potassium Compounds. These are of subordinate importance in the human economy, which fact may to a certain extent depend upon the nature of our food. Among the vegetable feeders, however, the serum of the blood still sIioavs a pre- ponderance of soda salts, and soda is also the base in their bile. But in many other portions of the system Ave find the most remarkable prepon- derance of potassium salts over those of sodium. Chloride of Potassium, KC1. This compound is found together Avith common salt in animal fluids; in * smaller quantity in man than in phytophagous animals. Its amount in the blood cells is however large (C. Schmidt), and in the juice of muscle it replaces chloride of sodium (Liebig). . Carbonate of Potassium, K2C03. Probably occurs Avith carbonate of sodium in some of the animal fluids, and in the urine of vegetable feeders in all probability as bicarbonate, KHCOs. Phosphate of Potassium, KH3P04, or K,HP04. It is not yet decided in Avhat form of combination Avith potassium ordi- 62 MANUAL OF HISTOLOGY. nary phosphoric acid occurs in the body, whether as an acid salt with one atom of base and two molecules of water, or a neutral as it is called, m which two atoms of base go to one molecule of water. The salt is met with in the juice of muscle (Liebig). Sulphate of Potassium, K2S04. Appears in the body, probably, with the corresponding salt of sodium and under similar circumstances. Ammonium Salts. The physiological processes of the body are attended by but a compara- tively small development of ammonia, so that in this respect they may be said to offer a contrast to putrefactive decomposition. The combinations of ammonium in the body are probably of various kinds; for the present, however, we are unable to enter into them very fully. Chloride of Ammonium, NH4C1. It is still an undecided question how far this or the carbonate appear in the economy. Carbonate of Ammonium. Is found in expired air, in decomposed urine, in blood, in the lymphatic glands and blood-vascular glands. The combinations which are here met 2CO ) with are the sesquicarbonate /-vttt \ w \ 04, and bicarbonate NH4.HC03. Iron, Fe, and its Salts. This metal is extensively distributed throughout the body, and occurs probably in all its parts. It is met with in various forms also, being sup- plied to the system in great abundance Avith the food. In some way not very fully understood at present, iron enters into the composition of the most important of all animal colouring matters, haemo- globin (p. 18). Uroerythrin and melanin also contain iron (p. 52). Protochloride of Iron, FeCl2. This salt is said by Brdconnot to be present in the gastric juice of dogs. Phosphate of Iron, Fe2P208. Another compound of iron generally accepted, though perhaps on in- sufficient grounds, as occurring in the living body. In regard to the presence of iron one thing is certain, namely, that all portions of the body supplied with blood must contain it It has also been found .in chyle lymph urine, sweat, bile, and milk, and finally in bair, cartilage, and other solid tissues. - Manganese, Mn. This metal is introduced into the system in company with iron and is met with here m minute quantity. It seems to be merely an accidenta constituent. It is found m hair, and in biliary and urinary calculi Copper, Cu. 2. ELEMENTS 0E STRUCTURE. A. The Cell. §45. Those anatomists of recent times Avho seek Avith the assistance of our improved microscopes an insight into the minute structure of the human and animal body, have all arrived at this conclusion, hoAvever widely their other scientific vieAVs may differ, that " the cell," cellula, is the most important of all the structural or form-elements of the system. This fact, although surmised by earlier observers, who recognised the structure in question under the name of " vesicle," was first firmly established by Schwann. Following up Schleiden's discoveries in vegetable anatomy, he shoAved the cell to be the starting-point, in the broadest meaning of the term, of the animal body (see above, p. 4). This is the greatest discovery ever made by the aid of the microscope. Present-day investigation tends more and more to confirm the correct- ness of this proposition of Schwann, that the cell alone, and by itself, must he regarded as the primordial structural element of our frame, and that all the various other elementary parts to be found in the mature body are originally derived from the cell. The first point, then, to be attended to here is, to obtain a correct im- pression of what is meant by a " cell," and what by a " structural element." By "form constituents," "form elements," "elementary parts," or " structural elements," Ave do not by any means understand (as might be incorrectly inferred from the terms) the smallest particles of the body re- cognisable by the microscope in the shape of granules, vesicles, or crystals. A form-element is rather the last, or—contemplating the subject from another point of vieAv, the first—anatomical unit: a combination of the most minute particles to form the smallest organic apparatus. Struc- tural elements are the first representatives of organic activity; they are, consequently, physiological as well as anatomical units; they are "living things." But Avhat is the cell? This question cannot be answered in a Avord, hut re- quires to be met Avith a someAvhat detailed description. The cell (fig. 40) is a microscopically small, primarily spheroidal body, which often assumes, however, other forms, and Avhich consists of a soft mass Fig. 40.—Two cells of round or oval form. a a, border of the cell; bb, cell body; c c, nuclei with nucleoli, d d. 64 MANUAL OF HISTOLOGY. including Avithin it a peculiar structure. These parts require special names. The soft substance mentioned is known as the cell-substance or cell-body (b b), the central structure enclosed Avithin it as the nucleus (c c), and a minute dotdike particle situated Avithin the latter again as the nucleolus (d d). The external boundary of the cell (a a) is in certain cases formed by the soft mass alluded to, or more frequently by a someAvhat hardened stratum, the enveloping or cortical layer, or, finally, by a distinct indepen- dent pellicle separable from the cell-body, and known as the cell-mem- brane. In regard to the latter, the views entertained respecting the animal cell have latterly undergone considerable change through the results of recent investigation. The presence of a special membrane was formerly con- sidered necessary (Schwann) to the conception of a true cell; but the frequent absence of this envelope and its relatively small physiological significance has been since recognised (Schultze, Brucke, Beale). But although its anatomical characters offer us the first and most important points in the definition of the cell, its physiological properties cannot be overlooked. By these the cell is constituted a living structure, endowed Avith special energies and the peculiarities of active vitality; Avith the power of absorption of matter, of transforming the same, and of excre- tion ; Avith the capability of groAvth, of change of form, and of cohesion or fusion with similar organisms. The cell possesses further, undeniably— although there may be a variety of opinion as regards the extent of these powers in individual cases—the capability of vital motion, as Avell as of proliferation, or the generation of a progeny. The cell, Ave repeat it, is the earliest physiological unit, the first physiological apparatus : it has been called an " elementary organism " with propriety. One of the most important facts established by recent scientific investigation is, that that mass from Avhich the bodies of all the higher animals take their origin, namely, the ovum, has entirely the nature of a cell, so that, consequently, each such animal body, he it ever so complex in constitution, once consisted of one single cell. While in this respect the latter must be regarded as the starting-point of animal life, naturalists again have brought to light creatures of such simple organisation that their whole body is formed of nothing more than one independent cell and whose whole existence is included within the narroAv circle of cell-activity Among such may be reckoned those animals known as grecrarines Finally, single-celled plants have been discovered by botanists, as°sincde- celled animals by anatomists : and even still more rudimentary or^ani^ma have been met with. ° Remakks-Compare the work of this author, « Mikroscopische Untersuchungen uber die Uberemstimmung m der Struktur und dem WanWh„™ aZ nu- S !J Pflanzen ;" also L. Beale, ''The Structure of the Simp™ Tissues of Z H™?T T- Lond 1861. But i. the cell the simplest "element^S<"Mtt structure which can meet all the requirements of the lowest grade ofhfeThis question may be negatived. An excellent observer E ffi*//fiPn«™iu w i i • Band 1, s. 269, Berlin, 1866; and Biologisch• Studlen& I Ie*5rP™°S?e. 1870), has shown that a particle of protoplasm, or "cvtode »Z hJ' ' ''.,LeiPzl»' for this. It is only subsequently, after the generation of 1 n , *!?*? ^ SUt?Cea becomes a cell. ll is, mSverthliess, a dL^ tJnMean? Jac't that tL^l? ^ raeySSDySieisb°die3 * ^ ^ " ™' ^^"^^ ELEMENTS OF STRUCTURE. 65 §46. Turning noAv to the more detaded analysis of cells, the first point to be borne in mind is, that the latter, in the earlier portions of their existence, manifest a certain amount of uniformity, whether as the cells of youn^ embryos or those of later life. Again, that in the course of further development they may assume, as mature and senescent structures, the most diverse shapes, as well as acquire an entirely different body, so that they not unfrequently take on an appearance which may remove them very far, nay, even so far as to be unrecognisable from the plan of a cell, given in the foregoing section. 1. Directing our attention, then, in the first place, to the size of cells, we find them, in the human body as well as almost everywhere in the animal kingdom, to be Avithin microscopic measurement. The smallest, such as Ave find, for instance, among the blood-corpuscles, have a diameter of only O-OOG-OOO? mm. (millimeters), Avhile the largest typical cell of our body, namely, the ovum, may attain a breadth of more than 023 mm. BetAveen these extremes the greater number of cells range in diameter from O011 to 0 023 mm. Those of 0 07-0T15 mm., such as occur, for instance, in fat and nerve tissue, must be looked upon as very large. Thus Ave observe that the most important structural element of our body is of remarkable minuteness, as usually met with. 2. If we next turn to the shape of the cell, Ave are struck likewise with its extreme variability. The fundamental form (fig. 40) is, hoAvever, spherical or spheroidal. From this primary form tAvo others, easily derived, are produced by compression and flattening in two opposite directions; these are the flattened and the tall narrow cell. Flattened cells springing from the spherical primary form by compres- sion are met Avith, in the first place (fig. 41), as disks, such as may be seen in human and mammalian blood-corpuscles; or they may become, by a further increase of superficial extent, fiat or scaly structures (fig. 42) such as those, for instance, of the epithelium of many parts of the body. Fip. 41 —Diskoid cells of human Fig. 42.—Flattened scaly epithelium cells blood, a, a, a. At 6, half side from the human mouth. view; ciose by at d, colourless corpuscle. That there may exist eArery gradation betAveen flattened cells and the spheroidal species appears self-e\*ident, and needs no farther comment. If the elements in question undergo, on the other hand, lateral com- pression, the resulting form may be either more or less cylindrical or conical, and the tall narrow cell is produced (fig. 43). We shall see later on, in our consideration of the several tissues, that many modifications of 66 MANUAL OF HISTOLOGY. this figure mav appear. The fusiform cell maybe regarded as one of inese^esXybeinPg narrowed, it is fined off at either end to a point (fiTht4fusiform cell usually gives off at either end a threaddike process; but'trfiLmente may oJciir in greater ^g^™^*^ and on their part undergo further ramification. It is in thib way that the sluale ell (fig. 45)° is produced-one of the most remarkable forms in which the structure in question can meet the eye. wsm Fig. 43.—Tall, narrow cells, as found in what is known as cylinder or columnar epithelium. Fig. 44.—Fusiform cells from immature con- nective tissue. Fig. 45.—Stellate cell from a lymphatic gland. 3. But far more important than either shape or size is the substance of the cell-body: in this the greatest variety is observed. Let us, take in the first place, young cells (fig. 46) : here we perceive that the body is made up of a more or less soft, usually viscid and slimy mass, containing in a transparent cementing medium a variable amount of albuminous and fatty granules (a-g). This primordial cell-substance is known at the present day by the name protoplasm (Remak and Schultze) borrowed from botany. It has also received from Beale, Koelliker, and Dujardin respectively, the names bioplasm, cytoplasm, and sarcode. The chemical peculiarities of this proto- plasm have been already referred to in § 12, and we shall be obliged presently to enter somewhat minutely upon the consideration of its vital properties. It will suffice to remark here, that it consists of an extremely unstable albuminous compound, insoluble in water, but which becomes gelatinous (or in some instances shrinks) on imbibition of the latter: it coagulates further at a low temperature and at death, so that only by the most careful manipulation can it be examined in a normal condition under the microscope. The amount of this protoplasm with which the nucleus is enveloped is very variable, and consequently the size and general appearance of cells. Our woodcut repre- sents from a to d elements with a medium amount of this substance; e, a larger proportion. Other cells are observed to possess but a very small quantity of pro- toplasm, as/ and g, without having lost the capability, however, of increasing in substance and subsequently fulfilling all the purposes for which cells in general are As far as we know at present, a cell can never again be formed lrom a nucleus which has quite lost its protoplasm But if Ave turn now to mature or senescent cells, we'frequently find tnat the protoplasm of an earlier period of existence is replaced by Fig. 4G. — Different kinds of cells with nuclei and proto- plasm ; half dia- grammatic. designed. ELEMENTS OF STRUCTURE. 67 matters of completely different characters; thus the body of the blood- corpuscle is found to be made up of a transparent yellow gelatinous sub- stance (fig. 47); m old scaly cells also, such as are met with on the surface of many mucous membranes (fig. 48), the protoplasm is replaced Fig. 47.—Human blood-corpuscles. Fig. 48.—Old epithelium cells from the human mouth. by a hard substance, poor in water, and almost destitute of granular matter, —a metamorphosed albuminous material, to which the name of keratin has been given. Such cells, however, as those in both instances cited, are no longer capable of supporting a prolonged existence, they have lost their active vitality with their protoplasm. Again, there are cells still more fre- quently met Avith which contain other substances as formed deposits in their pro- toplasm (fig. 49). Setting aside for the present those cells into whose bodies foreign matters, such as ,., granules of carmine (a), or blood-corpuscles (|j$? and fragments of the same (b), have pene- trated from Avithout (remarkable objects which will be considered at greater length presently), Ave frequently meet Avith globules and drops of neutral fats laid down in the original cell-mass (d), which may gradually coalesce, supplanting the protoplasm until but a small remainder of it is left. Besides such fatty matters, molecules of brown biliary pigment are to be seen in other cells, as, for instance, in those of the liver (c). Cells also Avhich have become the receptacles of melanin granules (p. 52) present the most peculiar appearance. This pigment may be pre- sent in such abundance that the Avhole body of the cell becomes black throughout (fig. 50). The occurrence of crystals in the interior of animal cells is less frequent. They are, however, to be met with as acicular for- mations, already alluded to (p. 27), and appear in the interior of fat cells on the post mortem cooling of corpses, within the membranes of the former (fig. 51). But while the appearance of these is by no means rare, there are other crystalline deposits Avhich are only encountered in minute quantity, and under abnormal pathological conditions. Matters which assume the crystalline form in such Avatery solutions as exist in the animal economy, must be regarded generally as unfitted to take part in the con- Fig. 49.—Cells with deposits of foreign matter in their protoplasm (half dia- grammatic), a, a lymph corpuscle with granules of carmine imbedded in it; b, another of the same, with included blood-cells and fragments of the latter c, an hepatic cell, containing fat globules and granules of biliary pigments; d, a cell with fat globules and distinct membrane; e, another, with granulesof melanin. 68 MANUAL OF HISTOLOGY. struction of tissues. The rarity of crystals as cellW^ta is thus explained by this law, as it may be called, to which, with all the vane Fig. 50.—Stellate cells containing black pigment. Fig. 51.—a b, Crystals of margarin; c, the same contained within fat cells; rf, a cell from adipose tissue destitute of crystals. ties of cells in the different groups of the animal kingdom, there are but feAV exceptions. §47. Among the further characteristics of the animal cell there noAV only remains for our consideration the envelope and nucleus. 4. The envelope. It has been already remarked that the protoplasm at the surface of the cell rarely remains so soft as in the interior. In general terms it may be stated that a hardening of the non-granular or free periphery of the cell usually takes place by contact with surrounding media (enveloping or cortical layer of protoplasm). This hardening is certainly, in numbers of cases, exceedingly slight, so that it is only to be recognised by the sharper outline of the cell: it can also be easily overcome, and softening again brought about by the very brief action of external agencies. In other cases, however, it is greater; the transparent, tough layer increases in thickness, and may be brought into view as distinctly separable from the richly granular protoplasm of the interior, by the action of water and other reagents. It is such appearances that have been over and over again accepted as proofs of the existence of cell-membranes, especially Avhen, through a rent in the cortical layer, the contents have been observed to protrude. And in fact, this hardened peripheral layer of protoplasm does lead us on to the cell-membrane as it becomes gradually more and more independent, and assumes different chemical properties. But no one is able to define where this cortical layer of protoplasm ends, and where the membrane of the cell begins—a point essayed on all sides in the case of animal cells at an earlier period of histological study. Occasionally, at some distance from the shrunken cell-body such a covering with double contour may be recognised (firr. 49, d) But its presence cannot be doubted for an instant, when, either mechanically as, for instance, by rupture and squeezing out of the contents, or by chemical reagents which dissolve the latter, the membrane is successfully isolated _ Ihose fat-cells already mentioned (fig. 51, a) allow of the fluid fat (6) being pressed out in drops, when such a membrane (c) becomes recognisable. Ihe same may he seen when the contents have been ELEMENTS OF STRUCTURE. 09 Fig. 52. extracted by alcohol. These membranes exist in many cellular formations of the body beyond question. Their purposes appear chiefly anatomical, in that the consistence requisite for many animal tissues is, as we know by experience, greater than could be yielded by the soft protoplasm of the cell- body alone. Where, hoAvever, the individual cells are widely separated by considerable quantities of solid intermedi- ate substance, or where just the reverse is the case, and they are suspended in a liquid, forming a fluid- tissue, this membrane is probably absent as a rule. Such cells are those of dentine tissue and of bone, as also the cellular elements of the blood, the lymph, and the liver (fig. 52). The membranes of cells are usually transparent, and, as far as we can see with our present optical instruments, structureless and Avithout open- ings or pores. Attention has, hoAvever, been lately directed to certain cells in Avhich pores may be distinguished by means of the microscope—a cir- cumstance into Avhich we shall have to examine more closely further on. It is probable, also, that in isolated cases this cortical layer or envelope covers only certain portions of the body of the cell. As a rule, Ave find the demarcation of a cell such that a smooth contour encloses the figure; but it may happen that the granular contents produce a rugged appearance on the surface, Avhich leads us inA'oluntarily to the dis- tinction between smooth edged and granulated cells (tig. 53, a d). Both of these differences are, hoAv ever, of minor importance. Again, owing to a par- tial exit of the matter contained within, the cell, which had been up to that time perfectly smooth, may assume a Avrinkled appearance ; while, on the other hand, the reverse may take place with a granulated cell through the imbibition of water; it may SAvell out and become a smooth rounded object. Attention has lately been directed by M. Schultze to a remarkable appearance in the borders of young cells, and especially those of flat epithelium; their surface, namely, is completely covered Avith points, ridges, and prickles, as they might be named (fig. 54), Avhich tit in among those of the neighbouring cells "like the bristles of tAvo brushes which have been pressed against one another." The appropriate name of " spinous and fumnced " cells has been given to these. 5. If Ave now turn to the analyses of the nucleus, with its adjuncts, Ave meet Avith a certain vari- ability in it likewise. First, the difference in size of the various animal cells brings with it very con- siderable fluctuation in the diameter of the nucleus; proportionately less, of course, than that of the cell itself. We may accept O0011-0"075 mm. as a medium diameter for the nuclei of animal cells ; but at the same time, it must be borne in mind that some may be found Fig. 53.—a b c, Smooth-eaged di.skoid blnod - corpuscles, with one granulated white cell (d) whose nucleus is ob- scured. ;%«^ "■i-Aty/^ riVftWWHl,,. Fig. 54.—Spinous or fur- rowed cells, a, from the undermo.-t layers of the human epidermis; b! a cell from a papillary tumour of the human tongue (copied from Schultze.) 70 MANUAL OF HISTOLOGY. Fig 55.—Two cells (a) with vesicular nu- clei at c, which show a smaller or larger nucleus at d. The nuclei themselves lie excentric in the body of the cell, 6. much smaller, even down to 0006 mm., and less, whilst other cells again possess nuclei Avhose diameter may reach 0-023-0-045 mm. The position of this nucleus in the animal cell is at one time central, at another excentric. The fundamental form of the object under consideration, as it is met with in the earliest formative cells of embryonic tissue, and frequently enough in those of more mature parts of the body, appears to be that of a vesicular body approach- ing the spherical figure (fig. 55, c c), with more or less fluid, and, it may be added, homogeneous, transparent con- tents and strong cortex, which latter shows, under the strongest micro- scopes of the present day, a double contour as optical expression of its thickness. Thus Ave see that the nucleus possesses an analogous structure to the cell, which is endoAved Avith a membrane, and one of Avhose components it is. In the interior of this hollow nucleus, or, as it has been named, nuclear utncle, or vesicle, may be discovered, single or double, a roundish formation, almost a mere speck on account of its minuteness: this is the nucleolus already mentioned (d d). This fundamental form, however, of the nucleus is fre- quently enough exchanged subsequently for another, alter- Fig.56.—Two cells ing thus its original appearance, although the variations muscie'a'a^the 0I" tne nucleus mav De stated as a rule to be less in propor- rod-Hk'e homoge- tion than those of the cell itself. We find, for instance, in turning to the consideration of some of these changes of figure, that it may become elongated, as in those cells which enter into the composition of unstriped muscle (fig. 56, b), or diskoid, as seen in the tissue of nail (fig. 57). Bamifications of nuclei have also been met with in certain cells of lower organism, but not as yet in those of the human body. tf§ Fig. 57.—Cells of nail tissue, a a, view from above, with the granu- lar nucleus; 6 b, side view of the cell, with the flattened levelled nucleus. Fig. 58.—Flat epithelial cells, with completely homogeneous smooth- edged nuclei. On the other hand, the nucleus may exchange the original vesicular condition of an earner period for solid contents, as is the case, for instance, in the superficial epithelial cells of the mouth (fig. 58) or for perfect homogeneity, so that even the envelope of the nucleus is no longer to be ELEMENTS OF STRUCTURE., 71 Fig. 59.—Two blood- cells of the frog, a 6, with granular nuclei, as they pre- sent themselves af- ter treatment with water. distinguished. This latter form is seen in the cells of involuntary muscle just mentioned (fig. 56, b). In such cases the nucleoli are frequently invisible. Itfcoften occurs also that elementary granules are laid doAvn in the nucleus, giving to it, Avhen in large quanti- ties, a rugged appearance, and precluding the possibdity, further, of the nucleolus being distinguished. It is thus that the so-called granular nuclei have their origin. Again, there are cells whose nuclei may be obscured by an enveloping drop of oil. The former may be seen on treating the blood-corpuscles of the lower vertebrates with Avater (fig. 59), Avhile the latter are of frequent occurrence among certain cartdage cells. It is not always that Ave are able to make out the object in question in the interior of animal cells: it is often hidden from view, as for instance, in the living cell. We have already men- tioned in a previous section that a rich de- posit of elementary granules also, or pig- ment molecules, may obscure the nucleus (fig. 60). The same may be the case if the cell-body be occupied by a quantity of fatty matter; but very close scrutiny will always reveal the nucleus ^to the observer after a time. On the other hand, there afre cells in Avhich such a covering up of the nucleus cannot be thought of, in which the contents appear perfectly clear, and yet in which Ave can by no means in our poAver render the nucleus visible. The coloured blood-corpuscles of mature mammalia and human beings belong to this category (fig. 61); likewise the cells of the more superficial layers of the epidermis Avhich clothes the external sur- face of the human body (fig. 62). But of both these Ave know that they possesssed nuclei at an earlier embryonic period. There are, consequently, certain cells in our system Avhose nuclei disap- pear usually at some period of their existence. We may also remark here and there in tissues whose cells are as a rule destined to retain their nuclei for the Avhole life of the animal to Avhose body they belong, an isolated cell Avithout a nucleus among its complete companions; but it must be looked upon as a rare anomaly. All such non-nucleated cells are moreover incapable of existing for any length of time, and are simply on their way to dissolution as far as we knoAv at present. * In contrast to the kind of cell just men- tioned, Ave meet with others in which two or even a greater number of nuclei exist. The first case (fig. 63) is seen with comparative frequency, and in very dissimilar tissues: cells Avith many nuclei are rare, and found principally in the medulla of bones, Avhere they may contain ten, twenty, or even forty nuclei, and 6 Fig. 60.—Stellate cells filled with black pigment. In two of the same we can recognise the nucleus, but in the third the latter is hidden by the quantity of melanin granules contained in the cell- body. Fig. 61. — Coloured human blood-corpuscles, a b e. Fig. 62.—Epidermis cells without nuclei. 72 MANUAL OF HISTOLOGY. at times attain Fig. 63.—Cells with double nuclei, a, from the liver; 6, from the choroidea of the eye; c, from a ganglion. the cell possess with certainty. enormous proportions (fig. 64). Such conditions are in- variably coincident with a process of proliferation in the cell, and will be treated of more minutely when discussing the latter. We must distinguish this.,truly double or multiple nucleus from another deceptive ap- pearance of two or several more in one animal cell. There are, namely, cellular formations in various fluids of the system, as in the blood (the white or colourless blood-corpuscles) lymph, chyle, mucus, pus, &c—we Avill call them lymphoid cells—Avhich contain originally a simple nucleus; Avhich Avhen mature may often, under the action of reagents, such as dilute acids, for instance, be made to break up into several pieces, so that the ob- server is deceived into the belief that he has before him cells with several nuclei. The question as to whether the body and nucleus of any further finer texture, cannot at present be answered §48. Turning now to the chemical constitution of the animal cell, Ave find ourselves entering upon a field of histochemical inquiry of which little is knoAvn: here more than elsewhere does microscopical research in the investigation of the elements of form appear to be far'in advance of chemical analysis. In order to follow up this line of inquiry Avith any hope of success, we should be able to separate the cell from its surroundings, i.e., from elements of tissue; to take it asunder, or resolve it into its various parts, i.e., inucleus, cell-body, membrane, and subject these separately to chemical analysis. Unfortunately this is for the present impossible, and thus the existence of a great gap in our know- ledge is more than sufficiently explained. We are in general only able to state so much; that the still very obscure group of protein com- pounds or albuminous principles, with its numerous members and modifications, with certain of the his- togenic descendants of the latter, play the chief part in the constitution of the animal cell. Besides these, as in all other parts of the system, Ave find as further constituents, Avater, and moreover usually in considerable amount; also certain mineral matters, and probably also everywhere fats. But though, after what has just been remarked, we may look on the protein matters, and their immediate derivatives, as those substances from Avhich the materials for the production of the animal cell are derived, chemical investigation teaches, on the other hand, that the various parts of the latter must be composed of modifications of'these, in that nucleus, cell-body, and membrane (when the latter is present) gener- ally display different reactions. Not unfrequently we are obliged to own our knowledge of the composition of animal cells as comprehended in these few and general propositions only. In some other cases, however Fig. 64. — Multinuclear " giant-cells " from the medulla of the new-born infant ELEMENTS OF STRUCTURE 73 and under favourable circumstances, it is possible to penetrate somewhat more deeply into the chemical constitu- tion of these most important of the ele- ments of form. Let us first, then, inquire into the constitution of the cell-body. We have already seen in one of the preceding sec- tions that this is originally formed of protoplasm. In speaking of the latter we described it as a tough, viscid, or . , , . . .. c ,. Fig. 65.— Lymphoid cells, 1-4, un- mUCOld Substance, consisting of a peculiar changed; 5, the nucleus and mem- albuminous Compound, which Coagulates brane; the same at 6,,7,and8; 9 the * ' ° nucleus begins to divide, also at 10 at death, and also when heated up to a cer- and ii; 12, it has broken up into six tain point; which becomes further swollen picceS! 13'free nuclei- up or gelatinised by the action of Avaterj but not dissolved. This is about all Ave know at present of this important compound protoplasm. The granules Avhich lie embedded in the homogeneous substances of the latter in greater or less quantity, consist partly of coagulated albuminous matters, partly of neutral parts, and more rarely of pigments, especially melanin. That mineral constituents are also present need hardly he remarked. In many cells the protoplasm is transformed gradually into various other modifications of the protein compounds. Thus, instead of it the mature blood-corpuscle is composed of watery haemoglobin, the formative cell of the fibres of the lens likewise of an albuminoid known as globulin. Other cells again contain mucin or allied substances, as for instance colloid, and it often occurs that the original cell-body is. converted by a loss of water into one of the more solid modifications of the albuminoid group, for instance into keratin, found in the older cells of epidermis and nail tissue, &c. However imperfect our knoAvledge at present may be, it must still be considered of importance to knoAV for certain that those more remote descendants of the albuminoids, as we meet them, for instance, in glutin and elastin (§ 15), never form the proper body of an animal cell. Ferments, also, are probably of frequent occurrence in the bodies of cells. Thus we find minute molecules of pepsine in the protoplasm of the glan- dular cells of the stomach, and allied matters in the elements of the in- testinal glands. We have also hydrocarbons presented to us in hepatic cells in the form of granules of glycogen (§ 16). Deposits of neutral fats are likeAvise of extremely common occurrence here. Granules and globules appear at first in the various kinds of cell- substance, gradually forming in seme cases large drops, which may eventu- ally displace almost the Avhole ofthe latter. And although it cannot be doubted that most of these fatty compounds are taken up into the body of the cell from without, it must still be regarded as extremely probable that a formation of fat can be brought about in the cell itself by the splitting up of its proper albuminous body. With the exception of the salts of lime, formed deposits of inorganic substances do not occur in the bodies of cells. In turning now to the consideration of the chemical constitution of the surface of the cell, Ave must remember that very generally the enveloping layer of protoplasm has been hardened, now more, now less, through con^ 74 MANUAL OF HISTOLOGY. tact Avith surrounding substances. As to the composition of this layer, as to its difference as compared to the softer protoplasm Avithin, Ave know at present nothing. Its power of resisting the action of reagents, such as acids and alkalies, is for the most part very limited. Further metamorphosis of this superficial layer leads on through in- termediate stages to the formation of the proper " cell wall." This appears to possess a far greater power of resistance, in that the albu- minous matter of the cortical layer has been converted into a substance, which in its whole demeanour as regards various reagents, and in its im- mutability, manifests a strong resemblance to, if not accordance with, elastin. Even years ago it Avas asserted by Bonders, that the membranes of all animal cells consisted of elastin; and although this expression of that most excellent observer may be someAvhat exaggerated, nevertheless the capability of changing into a cell membrane possessed by the cortical layer of protoplasm, gives support to the proposition that elastic matter (elastin) may take its rise from the protein substances, although the minutiae of the process of transition are not yet known. Passing on, finally, to the constitution of the nucleus, we have to dis- tinguish between the envelope and contents of this originally vesicular body. The contents, formed of a pellucid fluid, appear to be composed of some soluble modification of protein matter; for Ave can frequently pro- duce a precipitate of small granules in it, by the action of alcohol, acids, &c.', as, for instance, in the nuclei of ganglion cells, and that of the ovum. The envelope consists comparatively seldom of matter which does not resist the action of acetic and other allied acids, as, for instance, in the nuclei of the cells just mentioned. Usually—and this is the means for the recognition and distinguishing of the nucleus, lon<* in use empirically among histologists—the envelope of the latter and the remaining substance is not acted on by such acids. ]STow, although the substances in question correspond in the last respect with the elastic material of many cell-membranes, they yet differ from them most dis- tinctly in their greater or less degree of solubility in alkalies. This has been very properly pointed out by Kblliker to be a distinguishing feature between the nucleus and membrane of the cell. The chemical transformations Avhich the nucleus undergoes durino- the life of the cell are manifold, as, for instance, when it becomes solfd, or exchanges its vesicular nature for a granular one. The tendency, further of certain nuclei to deposit fats round about themselves is very'striking' a process which can go so far that, as is the case in certain cartilage cells, finally, instead of a nucleus, nothing hut # drop of oil can be distinguished. It is also remarkable that pigments are seldom seen in the nuclei of cells. Those of the epidermis of dark parts of the skin, however, appear to be tinged by some brown colouring matter. ° The nucleolus, owing to its minuteness, has almost completely escaoed chemical investigation hitherto. It is supposed, from its refracting pro- perties, to consist of fat. ° y Great uncertainty stiU prevails as to how far the products of the decomposition of histogenic matters (already discussed in a former section) which are found in the fluids saturating cellular tissue are originally constituents of the cell-body. It is also° impossibleo state even in the most favourable cases of simple cellular tissue, what products of decomposition belong to the different parts of the cell, what to the ELEMENTS OF STRUCTURE. 75 body, and Avhat to the nucleus, as in the case of the hepatic and con- tractile fibre-cells. If, as would appear from all this, our knowledge of the composition of the cell is very unsatisfactory from a qualitative point of view, how much more so Avhen we glance at it from the quantitative side of chemistry ! In fact, Ave are unable to give the quantitative analysis of any single form of cell in the body. §49. In regard to phenomena of vitality observed in cells, they would appear, in the first place, to be of the vegetative type—consisting in processes of absorption of matter, transformation and execretion of the same, growth and proliferation. Again, the vitality of the cell is mani- fested in the most striking manner by the extraordinary phenomena of contractility Avhich have recently been met Avith among the corpuscular elements of the animal body. Contractile cells have long been known—one might say as curiosi- ties—in the bodies of loAver animals. Comparatively recently they have been recognised also as existing very widely distributed among the same, and some animals are known of such simple structure that almost the whole mass of the body consists of them. But we have also gradually become acquainted with an ever-increasing number of the same kind of cells in the bodies of the higher animals, likewise endowed Avith the power of vital contractility. Besides this, such a property could no longer he doubted after the recognition of the fact that a widely-spread species of muscular tissue, known as unstriped, as also the heart (at least at an earlier period of embryonic life), had consisted of such cells entirely. Taking with all this the fact that, up to the present, this vital contractility has been observed in the cells of all but a feAv tissues, such as, for instance, those of the nervous system, we are almost war- ranted in concluding that, at an earlier period of their existence, all cells are endowed Avith this power of contraction; that is to say, as long as they consist of protoplasm alone, and before they are enclosed in a distinct cell-membrane, and that this power is dependent probably on some property inherent in the latter sub- stance. Let us take a someAvhat nearer glance at this wonderful phenomenon of cell life in individual cases. If Ave take a frog in whose eye inflammation has been produced by the action of nitrate of silver applied to the cornea, we find after a few days that the aqueous humour be- comes milky. A drop of this fluid, placed Avith extreme care under the F1g. 66.—Contractile lymph microscope, will often shoAv us the cells sketched in fig. 66 (pus-corpuscles). These seldom or never appear of simple spheroidal figure, but almost always under a variety of jagged shapes, Avhose points and angles are engaged in an incessant change of form, usually very sluggish, but at times someAvhat energetic. We are able to cells from the humor aqueus of an inflamed eye of a frog. 76 MANUAL OF HISTOLOGY. recognise also, that certain thin, thread-like processes, consisting of a clear structureless substance, extend themselves rapidly from the main mas3 (a), Avhile others much broader (b df) commence an extensive ramifica- tion (g h k). Should the branches of neighbouring processes come into contact with one another, they coalesce at the point of contact, forming net-like figures or broad flat meshes, which gradually assume the dark appearance of the rest of the body of the cell. Other prolongations of the protoplasm, on the contrary, have in the meanwhile receded and disappeared in the body of the cell. At times the most extraordinary intermediate forms of the cell result from these changes (/ e). All this time a slow circulation of the granules lying in the protoplasm may be observed, the nucleus moving about passively Avith them. It is only on the death of the cell that this extraordinary movement ceases, and that the former assumes the round shape (/), formerly supposed to be the only one in which the pus-corpuscle ever appeared. The species of cell just mentioned, our " lymphoid cell" (p. 72), is found Avidely distributed throughout the bodies of vertebrate animals, and has received different names, according to the region in which it is met with, as, for instance, the "white blood-corpuscle," the "lymph and chyle corpuscle," the " mucous corpuscle," &c. Does it undergo the same changes of form in the human and mam- malian body generally 1 This question may be answered in the affirmative; but, OAving to the much smaller size of the cell in the latter, and the rapid cooling of the preparation, the demonstration of vital contractdity is attended with more diffi- culty. The series of changes sketched in fig. 67 may be followed (a, 1-10) on the white corpuscles of the blood; but the energy of the movement is greatly increased if the natural Avarmth of the fluid be kept up artificially. Another instance of change of figure is depicted in fig. 68, which represents a small portion of living connective Fig. 67.—AVhite contractile corpuscles of tissue from the body of the fro" The human blood, a, 1-10, changes of shane 11 1 ±- ■ °" succeeding one another in a cell within a CUlt3 Known as COlinectlVe-tlSSUe COT- stee,iiradteYO DCO l/lirtli Kilo iiumjn """ ""» "~ —--- origin in the cavities of coalescing cells, but is rather an intercellular space. 98 MANUAL OF HISTOLOGY. § 61. As Ave have just seen, the intercellular matter between the formative cells of the capillaries appears in the most minute quantity, reminding us of the allied tissue epithelium (fig. 81). . But it is otherwise in certain textures which, though appearing under great variety of changeable forms, are yet connected by intermediate links, and merge at times from one variety into another. These must be regarded, consequently, as members of one natural group, and are known as the con- nective substances. Cartilage, the consideration of which occupied us in a former section (§ 53), is one of these ; further, colloid reticular and ordinary connective tissue, fatty, bony, and—nearly related to the latter —dentine tissue, must be also reckoned as belonging to them. In all those various forms in which the members of this Avidely-spread groap of connective substances appear, we meet with cells imbedded in more or less abundant intercellu- lar substance. The cells, however, display very different characters in different instances, and no less so the intercellular substance, which may he found either in the form of mucoid jelly, fibrous, and more solid substance, or of hard stony Fig. 101.—Tissue of the vitreous humor of a hu- matter. man embryo of four months old. ^ vitreous humor of ^ fcetal eye affords a beautiful example of an extremely simple texture (fig. 101). Simple nucleated cells lie here in a watery jelly. If Ave can imagine the latter replaced by a solid mass of chrondin, we have the Avell-known appearance of cartdage (fig. 83). It is seldom, however, that in the group of tissues under consideration the cells remain in an abundant intercellular substance, so slightly matured, as in cartilage. Crowded together, they may perhaps increase in size, and, retaining their spherical shape, become filled with neutral fats, as is the case Avith fat-cells which have this origin, as far as is known at present. But, as a rule, the forma- tive cells of the connective-tissue group abandon the spheroidal form, and grow irregularly. At one time they become fusiform by extension in Fig. 102.—stellate cells tAvo opposite directions, as we have seen in a similar case, though on a far larger scale, among the elements of involuntary muscle (comp. fig. 96, p. 95) ; at another they assume more or less of a stellate form (fig. 102). And, just as certain connective-tissue cells may become fat-cells, so at this stage of development many pigments may be laid down in their bodies, terminating their transformations. It is in this way that the structures known as stellate pigment-cells are formed (fig. 50, p. 68). In their further progress in development, connective-tissue cells mani- fest, besides a tendency to continuous elongation, an inclination to fuse with one another. In this way, by the cohesion of the processes of adjoining cells, extremely delicate cellular networks are formed (fig. 103), whose meshes are occupied by a mucoid jelly. But this latter may again disappear, and be replaced by totally different matters, as, for instance, by lymph-corpuscles. As they grow older, also, connective-tissue cells, tense and full when young, may shrink and decrease very considerably in volume But, as already mentioned, the variety Avhich the intercellular substance ELEMENTS OF STRUCTURE. 99 of connective tissue presents for our consideration is not less consider- able than that existing among the cells themselves. Consisting originally of albuminous matters (con- sistently with its origin from the protoplasm of the cells), it commences later on, as its solidity increases, to contain glutin, or more properly, collagen. In bone again, and in dentine, it attains a high degree of hardness and firmness by the reception into its composition of large quan- tities of the salts of lime. It is not, however, changes alone of this kind in consistence and composition Avhich are to be met Avith in the intercellular substance of the connective-tissue group. Even if it escape solidi- fications of the species just described, it still manifests a great tendency to become streaky or banded, or. finally to break up into fibrillar Again,* between all these varieties no very distinct boundaries exist; and in the neighbourhood of banded or fibrillated portions, we may encounter more or less of a residue, as it were, of unchanged homogenous intercellular substance. The fibrilke alluded to are sometimes found in the form of extremely fine isolated threads, but are usually arranged in bundles. They are known as con- nective or cellular-tissue fibrillaB. Fig. 101 is designed to represent the latter. In the preparation, which is from a structure intermediate between true cartilaginous and connective tissue, we find simple cartilage cells scattered among bundles of fibres. In hg. 105 also we have these fibres (/), (grouped in bundles at (g)), between stellate con- nective-tissue cells (a-e). But this metamorphosis of the for- merly homogenous intercellular mass into collagenic fibres is not the only one met with in connective tissue. Another kind of thread-like element, consisting of a material with far greater power of resistance to reagents (comp. § 15), is formed by the transformation nf intercellular matter, and is known as Ot lntercenuidl iiict , y. i Fig. 104._Fibrous cartilaginous substance the elastic fibre (hg. 100, ll). It aiSO fr»m aVigamentum interveitebraleof man is liable to vary much, both as regards strength and the occurrence or absence of branches (fig. ™bh However this appearance of elastic matter in the form of fibres is not the only one it makes in connective tissue. The nterce hilar matter may be transformed, at the boundaries of the tissues in question, towards the cells and cellular networks, and likewise at their surfaces, &c (but till re aining its homogenous appearance), into limiting layers of divers kinds formed of a substance identical with, or optically and chemically the same as elastin. These have frequently been erroneously taken for cell-membranes and other peculiar envelopes. Thus in the course of development of connective substance, a whole Fig. 103.—Cellsfrom the enamel organ of a human foetus at four months. 100 MANUAL OF HISTOLOGY. series of the most striking transformations takes place in an originally purely cellular tissue. §62. Another series of metamorphoses which may be mentioned here leads, it is supposed by a process of fusion, to the formation of many of the final ramifi- cations of nerve-fibres. But the mode of origin of the unbranched nerve-fibres situated in the middle of nervous trunks (fig. 107, 1) is still, it must be granted, a most obscure point. Nerve-fibres are usually observed to divide in binary order when near their ter- mination (fig. 108). At such points (at least appar- ently) are situated stellate cells, with usually three processes (fig. 107, 2 a1, b1, b"), one of which is lig. 105.—Connective tissue from between the muscles of the .. ,' , „ . . , leg of a frog, a-e, connective-tissue cells; /, fibrillar; and United by fusion With the g, bundles of the same; h, network of elastic fibres. upper unbranched portion of the fibre, thus preparing the way for ramification of the latter, j The neurilemma, or primitive sheath, a structureless tube Avhich envelopes the mature nerve- fibre (fig. 108), is probably, as in the case of the sarcolemma of muscle elements, laid down from adjoining structures. §63. The physiological relations of the remaining tissue ele- ments originating in the meta- morphosis of cells, dealt with in the second division, are so very various that they must, for the most part, be reserved for future consideration. In muscle-fibres and nerve-tubes we have tissues of the highest physiological dignity, Avhile the great group of connective substances takes but a low rank as investing or support- ing tissues for the system. . A. ..„ The capabilities of transmuta- tion are very various in the different tissues derived from the cell- but at present our knowledge of the details of this subject is very imperfect Muscles and nerves, we are aware, are remarkable for the energetic Fig. 106 —Elastic fibres from the human body. a. simple and of the liner kind; c, a thick one, branching- 6 fibrous network. " ' ELEMENTS OF STRUCTURE. 101 transformation of material which goes on in them, although the nature of the processes is only known as regards the striped fibre. In contrast to this, many connective- tissue parts are remarkable for the great permanence of the sub- stances of which they are consti- tuted, especially Avhen they are only scantily supplied Avith blood- vessels, and possess numerous elastic fibres. In other struc- tures of the same kind a very rapid transmutation of material may take place, when a large amount of blood passes through them, or when they are finely canalised, as for instance, in the case of bone. On the other hand, all connective-tissue structures display an enormous degree of energy in a formative direction under conditions of pathological irritation, and are thus of great Avorth in the plastic processes of the diseased body, considerations which will occupy us again in a subsequent section. Fig ^.-Development * nerve-fibres in the frog. In regard to the products of transmutation much has been already said. We refer the reader to pp. 21, 22 for the glutin-yielding sub- stances ; to pp. 40-50 for the alkaloids. The voluntary or striped muscles, consisting of albuminates, yield as decom- position products, kreatin, krea- tinin, hypoxanthin, inosinicand lactic acids, and inosite. Of the physiological decay of the form-elements, and the regeneration and length of exis- tence of the same, we knoAV very little, excepting in the case perhaps of striped muscle- tissue. The duration of many of them, as for instance, of elastic fibres and allied struc- tures, is probably long, for in their case we have only remain- ing the processes of solution and degeneration, mechanical attrition being excluded (comp. p. 94). The three kinds of transformation, by pigmentation, deposit of fat (fig. 109), and of cal- Fig. 108.—Small branching nerve-fibres, a and b, from the mesentery of the frog, surrounded by thick envelopes studded with nuclei; 7, the trunk; 2 and 3, the branches. 102 MANUAL OF HISTOLOGY. Fig. 109.—Human mus- cle-fibre undergoing fatty degeneration. careous matters in cells, may at least be partially regarded as physiological processes, but belong probably, in the elementary parts with which we are now engaged (like many other modes of degeneration), 1 e in a great measure to the pathological changes of the system. Later on we shall be obliged to enter more fully into the consideration of this subject. §64. ISTow, by the combination of structural elements of similar or dissimilar kinds, and in larger or smaller quantity, the various tissues of the human and animal body generally are formed. These are naturally regu- lated as regards their anatomical texture, chemical constitution, and physiological properties, by the ele- mentary parts of Avhich they are composed. A classification of tissues that shall have any scientific value is still a matter of the greatest dif- ficulty—nay, Ave might almost say, of impossibility. Such a classification, namely, can be founded only on a knoAvledge of the mode of development of the structural elements. But histogenesis, unfortunately, although com- manding a considerable amount of material in many branches of our science, is yet but very imperfect in others. The history of the origin of tissues is, as a whole, not far enough advanced to enable us accu- rately, and without being obliged to resort to many hypotheses, to trace the outlines of a scientific classification of the various tissues. Even that apparently easy and accurate division into simple and composite textures cannot be strictly adhered to, and the question Avhether we have before us a composite tissue or not must, in many cases, be decided according to individual opinion, as to whether certain metamorphosed portions of the ground-substances are to be considered as structural elements or no. The following classification, therefore, is only to be accepted as pro- visional, being designed (as is usually the case in artificial systems) more to bring in review in a certain order the materials to be considered, than ahvays rigidly to associate together parts probably related to one another in their mode of development. The practical objects aimed at in this work will render it necessary, besides, to consider many things together, Avhich logically should be dealt with separately. The folloAving is our division :— A. Tissues composed of simple cells with fluid intercellular sub- stance. 1. Blood. 2. Lymph and Chyle. B. Tissues composed of simple cells with a small amount of solid intercellular substance. 3. Epithelium. 4. Nail. ELEMENTS OF STRUCTURE. 103 C. Tissues composed of simple or transformed cells (in some cases cohering), situated sometimes in homogeneous, sometimes fibrous, and, as a rule, more or less solid intermediate substance (Connective-tissue Group). 5. Cartilage tissue. 6. Colloid do. 7. Beticular connective-substance. 8. Adipose tissue. 9. Connective do. 10. Bone do. 11. Dentine do. D. Tissues composed of transformed and, as a rule, non-cohering cells, with scanty homogeneous and more or less solid inter* mediate substance. 12. Enamel tissue. 13. Lens do. 14. Muscle do. E. Composite Tissues. 15. Nerve tissue. 16. Gland do. 17. Vessels. 18. Hairs. 8 n. THE TISSUES OF THE BODY. II. THE TISSUES OF THE BODY. A. Tissues composed of Simple Cells with Fluid Intermediate Substance. 1. The Blood. §65. In the blood-vessels of our body, a closed system (except in the case of the spleen) of intercommunicating canals, into which, however, the lym- phatic and lacteals discharge their contents, there exists an extremely com- plex fluid, " the blood," which is constantly in motion during life. And just as on the one hand no pause takes place in its continuous circulation while life remains, so on the other hand is this fluid unceasingly engaged in a lively interchange of matter. The walls of the blood-vessels being formed of membranes permeable to endosmotic currents, and processes of filtration further occurring in glands, the blood is constantly being robbed by the organs and tissues of certain of its constituents in the form of watery solutions, Avhile other substances similarly dissolved are rendered back to it again. It receives also bulky additions of other complex fluids in the shape of lymph and chyle poured into it. Notwithstanding this coming and going of material which constitutes the blood the centre of the vegetative processes of life, the fluid in ques- tion is always singularly unvarying, both in regard to chemical and ana- tomical composition, any deviations from the normal standard being rapidly compensated. Human blood is a thickish, opaque fluid with a peculiar faint odour, alkaline reaction, temperature of about 38° C, and a red colour,—light cherry-red in the arteries, but someAvhat deeper in the veins. The amount of blood contained in any one body cannot be estimated at present with anything like accuracy, and Ave find statements on this point very various as regards the human system. It appears probable that the weight of the blood averages in man about a twelfth or thirteenth of that of the Avhole body. Remarks.—Compare Nasse's article "Blut" in the Hundwbrterbuch6Ct6Q. TISSUES OF THE BODY. 125 It has been maintained by Nasxe and Harless that a change of form is produced in the red cells by the action of carbonic acid and oxygen gas, the latter decreasing its size, the former causing it to SAvell out. This has been doubted by others, but has again received support from recent observers. Many other things may also act on the colour of the blood, modifying it; for instance, an abnormal preponderance of colourless elements may produce a lighter tint in the fluid. Thus leucaemic blood often appears strikingly changed. Sinking of the blood-cells.—The coloured blood-corpuscles possess, as has been already mentioned, a considerably greater specific gravity than the intercellular fluid—about as T105 : T028 in man. They Avould always, therefore, sink rapidly to the bottom in a vessel containing blood, or indeed in any quantity of the same in a state of rest, in obedience to the laws of gravity, Avere it not that the rapid coagulation of the fibrin ren- ders this in most cases impossible. This gravitation, hoAvever, of the cells does to a certain extent take place in blood coagulating slo\Ady. But the process may be distinctly folloAved up in blood deprived of the poAver of coagulation, by being beaten up or mixed Avith other reagents. Here Ave may perceive, after a considerable time, the commencement of a separation of the Avhole mass of blood into two portions—a superficial, almost colour- less, transparent layer of fluid, and a red mass of coloured cells, occupying the floor of the vessel. Microscopical examination shows that the second element of form, the lymphoid cell, has taken no part in this gravitation, being a lighter body. Comparison of examples shoAvs, also, that this sink- ing of the red cells commences sometimes rapidly, and often after some little time. The position which the blood-corpuscles of human beings and mam- malia (but not those of the other classes of vertebrata) take up in this state is peculiar. Instead of floating about singly in the fluid, as was the case during life, they now lie together with their broad surfaces in con- tact A\dth one another, forming aggregations (fig. 122, e) like rouleaux of coins. If Ave follow up this formation of rolls, Avhich .begins even in a drop of blood freshly taken from a vessel, and observe it from its commencement on under the microscope, the pro- cess is seen to be initiated by the coming together of pairs of cells, which then cohere by their broad surfaces. From this on, tiie rouleau grows rapidly by the addition of new members, and it frequently comes to pass that other little Columns, Or rouleaux, range them- *"*■ 122.-Human blood-cells; e, formation of . op i rouleaux. selves Avith the first-formed at various angles, giving rise to the formation of dendroid, and often almost net-like figures. The addition of Avater at this stage of the process dis- 12G MANUAL OF HISTOLOGY. members the rouleaux, in that the several cells swell out and assume the spherical form, and thus again separate from one another. On this account the roundish corpuscles of the blood of the hepatic and splenic vein show no such columnar grouping. The cause of this formation of columns is still unknown. I he explana- tion of the phenomenon through the adhesiveness of the intercellular _ fluid or surfaces of the cells does not suffice. At all events, it favours the descent of the coloured cells essentially, for the little structures thus united must be able to overcome better than when isolated the resistance offered to their gravitation by the fluid. If rouleaux have once been formed, the same settling down makes itself again rapidly evident in blood Avhich has been.re agitated. Remarks.—It is a striking fact that, on the addition of anything which renders the intercellular substance more dense, as, for instance, of concentrated solution of sugar, the settling down of the blood-cells is accelerated, although just the contrary might be expected. §79. Coagulation of the blood.—The consistence of the blood begins very rapidly to change a few minutes after it has been obtained from the vessels—it coagulates, namely. This process commences much more slowly Avithin the vessels of the corpse, or in sanguineous effusions in the interior of the living body. The latter may preserve their original consistence for many Aveeks. Now, as regards the phenomenon itself—first of all, we remark the com- mencement of this change in blood taken from the living body in from two to five minutes. The first step in the process is the formation of a thin pellicle of the greatest delicacy on the surface of the fluid, Avhich soon acquires greater thickness and solidity, so that it may be at length lifted off with the point of a needle. Commencing thus on the surface of the fluid, this formation of mem- brane extends itself gradually along the sides and down to the bottom of the vessel—in fact, at every point at Avhich our sample of blood comes in contact with the latter. The consistence of the blood so enclosed then begins to change ; it becomes firstly somewhat thickish, like a half-cooled solution of glue, attaining not long after the consistence of stiff jelly, or of a saturated cold solution of glue. Then, at the end of from seven to fourteen minutes the blood has lost all its fluidity, and has been trans- formed into a thoroughly solid mass, Avhose form is determined by that. of the vessel in which it is contained. This is, hoAvever, by no means the end of the process. The solid jelly, overcoming the adhesion to the Avails of the vessel, contracts subsequently more and more, pressing out a part of the fluid which has been entangled in it by the coagulation. The commencement of this contraction takes place tolerably early, but it only reaches its termination after a compara- tively long period, ranging from tAvelve to forty-eight hours. At first there appear on the surface of the coagulum a few drops of a transparent fluid; the number of these soon increases, upon which they coalesce, form- ing larger drops, and at last run together into a layer of fluid Avhich covers the surface of the coagulated mass. Whilst the coagulum thus pro- gressively contracts to a smaller volume, similar layers of fluid to that on the surface collect under the latter, as well as along the edges and floor of the vessel, until the mass which at first adhered closely to the TISSUES OF THE BODY. 127 cup, so that the latter could be turned upside-down Avithout its falling out, commences to float in the expressed liquid. From this on, the process only undergoes a quantitative alteration—that is, a continuous contraction of the lump causes it to decrease more and more in size, at the same time that an ever-increasing quantity of fluid is being pressed out of its interstices. When the Avhole process is at an ' end, Ave have a larger or smaller coagulum, sometimes soft and sometimes hard, floatin" in a varying amount of transparent fluid, Avhich has, like the plasma, a slight yellowish tint. The coagulated mass having con- tracted uniformly, preserves the figure of the vessel, and forms a diminu- tive cast of the same, appearing in an ordinary porcelain basin plano- convex, and in a test-tube cylindrical. Its colour is that of the blood,— of a darker red, however, at the lower and internal portions than on the surface, Avhere it is light. This red lump has received the name of the crassamentum or placenta sanguinis, Avhile the fluid in which it swims is known as the serum, or serum sanguinis. Now, Iioav are these two portions of the coagulated blood related to that which circulates in the living body, to its cells and intercellular substance 1 . We must remember, in the first place, that the latter is a fluid con- taining the two constituents of fibrin in solution. And as in other cases, so also after withdraAval of the blood from the system, these combine to form coagulating fibrin, by which, in that the fibrinogen is sufficient, the whole fluid, together Avith its cells, is entangled by the* solidify- ing mass; just as a solution of glue retains, on cooling, any par- ticles which may have been sus- pended in it—to make use again of this ordinary simile. By the progressive contraction of the gelatinous mass, a part of this noAV defibrinated intercellular fluid is expressed in ever-increasing pro- portion from its meshes, Avhilst the blood-cells remain behind en- tangled. From this Ave see that the liquor sanguinis consists of inter- cellular fluid deprived of its fibrin, or is, in other Avords, defibrinated plasma. The Crassamentum must Fig. 123.—Human blood-eells ; coagulated fibrin at d. 1 ., 1 o 1 c i\ with included corpuscles. consequently be formed of the blood-corpuscles entangled in coagulated fibrin. And, in fact, microscopical examination of thin sections of the placenta sanguinis sIioavs us the unchanged cells embedded in a homogenous, fibrinous, or plaited sub- stance (fig. 123, d). Of course a more or less considerable quantity of the intercellular fluid must still remain entangled in the cake of blood. According to what has just been remarked, serum shares Avith the plasma its transparency, light yelloAvish colour, and chemical characters. Its specific gravity must, however, be somewhat loAver, and may be stated at between T026 and 1-029. It not unfrequently happens that a 128 MANUAL OF HISTOLOGY. certain number of the red corpuscles escape being entangled in the coagulum, appearing as a kind of reddish sediment in the lower strata of the serum. When a quantity of blood is beaten and Avhipped up, the fibrin deposits around the instrument used, and the former remains fluid. In such defibrinated blood the sinking of the red corpuscles mentioned in § 78 may be best observed. §80. The process of coagulation of blood, moreover, displays much variety. The consideration of each several point connected Avith it in detail, hoAv- ever, Avould lead us too far here ; Ave Avill only, therefore, touch on some of the most important matters of interest. As regards the rate at which the changes take place, Ave find that they may be hastened or retarded. Betardation is easiest produced, as a rule. The coagulation of blood is accelerated by setting the fluid in rapid motion, as, for instance, by means of whipping or beating. The blood of men is said to coagulate in general more slowly than that of women. Further, arterial blood solidifies more rapidly than venous, Avhose greater amount of carbonic acid exercises a retarding influence on the process. Again, atmospheric air accelerates the clotting of blood, which explains the fact that, the finer the stream of blood flowing from the orifice of a vessel, or the flatter the dish in which it is caught, the more rapidly does it become solid. Hewson's experiences, also, are in harmony with this, who found that air injected into the vessels of a living animal frequently furthered coagulation. However, we may prevent the access of air to the blood of a dead animal with all caution, without being able to preserve it in a fluid state. Thus we see that it may coagulate without the influence of the oxygen of the air, as it does also in an atmosphere of carbonic acid, hydrogen, or nitrogen gases. As to the influence of temperature, Ave find that warmth favours the process m general, Avhile cold retards it. Coagulation may take place at any point above freezing, and if we subject fluid blood to the action of great cold it may be frozen before coagulation sets in, subsequently under- going this change on being cautiously thawed. How far changes in the composition of the blood may influence the rate of coagulation has not yet been sufficiently accurately ascertained. One important item m the process appears to be the nature of the fibrin itself Ihus the blood of certain animals, as, for instance, of the horse, solidifies slowly, whilst that of the sheep does so more rapidly The annals of medicine also record extraordinary cases of extremely late coagu- ation, which are probably only to be explained likewise by some modifica- tion in the constitution of the fibrin. y moa™a The character, also of the crassamentum is liable to vary greatlv some- times it is uncommonly small and hard, sometimes large, soft, and fracude Poorness in corpuscles may cause the first of these states, an increase in the latter the second m that a superabundance of cells-other thinS being equal-must be looked on as a hindrance to the contraction of Jh fibrin, Avhilst in an opposite state but slight resistance to it is offered t^^T ^ ^^ °f ^^ * th6 bM ^ves rise lot Beside all this, there occur also verv innnm,>lnfQ „ * where the proeess remains slation^> %7%>£~ feffl TISSUES OF THE BODY. 129 we see that very soft fragile clots may subsequently become again fluid. Finally, in some portions of the system the blood does not undergo this change at all, as, for instance, in the hepatic vein, and also possibly the menstrual blood of the female (p. 121). The blood of persons struck by lightning, and of those dead of asphyxia, has been found fluid in toto. If in the moment of coagulation the coloured cells have already disap- peared from the uppermost layers of the fluid, the coagulum does not present the usual red colour, but is yellowish Avhite in its superior por- tion, then knoAvn as the crusta phlogistica s., inflammatories Micro- scopic examination of the latter shoAvs the absence of red corpuscles in the coagulated fibrin, and, on the other hand, the lymph-corpuscles Avhich are specifically lighter imbedded in the loAver part of this light coloured stratum. And in that a quantity of cells usually hinders the contraction of the fibrin, the latter shrinks with much more energy in this uppermost layer, Avhich is poor in the former, than in the parts of the cake Avhich are of a deeper red. This explains the fact, that the crusta phlogistica generally forms a concave disk depressed in the centre, and smaller than the red part of the placenta lying underneath it. This buffed portion then is produced, on the one hand, by the more than usually rapid gravitation of the red cells, or on the other by delay in the coagulation of the fibrin. Thus we meet it as a normal appearance in the blood of horses. It is met Avith frequently, likeAvise, in the human being as a pathological phenomenon, and especially during inflammatory dis- eases of the respiratory apparatus; hut also under more normal conditions, as, for instance, in the blood of pregnant Avomen. OAving to our ignorance in regard to the protein substances, this pheno- menon of coagulation cannot be at present explained. Since the earliest days of medicine, however, there has been naturally no lack of efforts to do so. The cooling of the mass of blood, its coming to a state of rest, or the action of oxygen on it, have all been looked upon as the causes of the process. ^Recently Briicke has entered the lists in defence of an old theory formerly held by A. Cooper and Thackrah, namely, that the blood is retained in a fluid state by contact with the internal surface of the living heart and blood-vessels. A. Schmidt also ascribes to these surfaces the property of retarding coagulation^ This is the present (but let us hope temporary) state of our knowledge on this point. §81. If Ave noAv ask, at the conclusion of this long inquiry into the nature of the blood, How much is knoAvn at the present day of the conditions during life of its tAvo species of cells? Ave must allow that the results of all research so far are but very unsatisfactory. The red cells are the vehicles for the oxygen of respiration, and appear to generate haemoglobin within them, and to contain fibrinoplastic matter. The physiological destruction of these cells takes place, firstly, in the blood passing through the vessels of the liver, taking a part there in the production of the bile, as is indicated by the solvent poAver of the alkaline salts of the biliary acids (p. 108), as also the near relationship betAveen haemotoidin (§ 35) and bilirubine (§ 37). Again, Ave meet Avith another species of decay of the blood-cells in the more quiescent blood of the spleen, Avhere they form small aggregations, which are transformed gradually into dark pigmentary masses. Forced 130 MANUAL OF HISTOLOGY. into the amoeboid lymph-cells of the splenic tissue, the corpuscles and their fragments may give rise to the formation of those cells containing blood-corpuscles observed in the spleen. The same may also take place possibly in the medulla of bones. We may mention here another circumstance for the discovery of which Ave arc indebted to Strieker, namely, that by impeded circulation and increased pressure the red cells of the blood are forced through the unin- jured Avails of small vessels (capillaries and veins). Thus partly unin- jured, partly divided into small beads, in consequence of being obliged to squeeze through, they reach the exterior, and are found in the neigh- bouring tissues and adjacent lymphatic passages according to Hering. In the first position they probably decay very rapidly, while their occur- rence in the latter explains, at least partially, the presence of red blood- corpuscles in the lymph, already long known. It is only seldom that under normal conditions blood escapes into the tissue of any living organ from lacerated vessels; but we have one case, that of the ruptured Graafian vesicle. Such extravasations, however, are not of unfreque.nt occurrence pathologically. In both these cases we meet ^^o^^boX^^^^^ ^1 h0U,"S *ft«™ta«on baa been set up, showing alreSdy escaped. I a ve^n a Ihe Ivnmhn^'i^' f°V at ?■ ^ mode of escaPe of cells> at 6' som« throng; 5, LtnVjX' vessel; t&^^S^S!^ ^ ** "^ "* ™^ ** ™* from fhfrtT °f fc+he,C0l°Ured e!ementS after coaS^tion, and production mT tZ f""" ^ ^^ In SUch effusions of bl0°d> also, we corpuscles * * ^^ mentioned containing blood- lvm nhX10^!? C6llS deriV^d ?°m fche medulla of bone^ the spleen, and ymphatic glands, are now looked upon, and indeed rightly, as se vin» to replace the loss of the red corpuscles (§71) *' bervm° But in what proportion these undergo transformation into the latter is rme^orowr^f"11^™! H°WeVer' We Cannot doubt that su<* RiwfTZ P , white corpuscles into red does take place very exten- sively after severe losses of blood, where a rapid reparation occurs But these lymph-corpuscles have yet another destiny TISSUES OF THE BODY. 131 Like the red cells, they also (but by virtue of their vital contractility) pass through the uninjured Avails of the vessels (fig. 124) in the healthy as well as the diseased body; in some cases re-entering the lymphatic cir- culation, in others penetrating into various tissues (§ 49). Now it is probable that partly, at least, from this source the wandering lymphoid •cells of connective tissue have their origin. These Ave Avill make the sub- ject of later consideration. Under conditions of inflammatory irritation such an exit from the blood-vessels in the vicinity of the affected part takes place on a large scale (.4. Waller, Cohnheim), and the pus-corpus- cles appearing at this spot are, in part, nothing but the lymphoid cells of the blood Avhich have emigrated. Finally, touching the origin of the blood in the embryo, Ave may pre- mise by stating that Ave are but partially acquainted Avith this chapter of histogenesis. But in order properly to comprehend the process, we must first render ourselves familiar with the broader and more important outlines of embryology generally. By the processes of segmentation in the impregnated ovum a cellular material is formed Avhich represents the germ, i.e., that spot at which the body of the coming being is to be built up. It is first disposed in the form of a membrane Avhich, according to Remak's admirable investigations (recently questioned, hoAvever), may be distinguished as made up of three layers of cells arranged one over the other, from each of which certain distinct tissues and organs have their origin. Thus we have a key to a scientific classification of the tissues of the body. For the present it need only be borne in mind that the upper stratum bears the name of the "corneous," the lowermost that of the "intestinal gland " layer (Darmdriisenblatt). The derivatives of each of these will be met Avith presently. From the intermediate leaf knoAvn as the "middle ger- minal" layer very many structures take their origin; thus, the Avhole of the large connective-substance group, the voluntary and unstriped muscles, the vascular and lymphatic systems Avith their accessory organs and con- tents, including the tissue under present consideration, the " blood." The first formation of blood then takes place at a very early period in foetal life. But the primary blood-cells are not related in any Avay to the characteristic corpuscles of later times, they are nothing but what are known as the ordinary formative or embryonic cells of which originally the most Avidely different structures of the body may consist. The first appearance of the primary blood-cells corresponds with that of the heart and larger vessels immediately adjoining it. Both of the latter are said not to be originally holloAv, but solid aggregations of cylin- drical form, consisting of cells. Noav the destiny of these cells entering into the formation of the cylinders is various; the peripheral become ad- herent to"0ne another, or unite more closely still to represent the primitive walls of the heart and vessels, while between the most internal, bordering on the axis, fluid gradually accumulates in such quantity as eventually to immerse the cells completely. From this moment on we may Avith propriety speak of blood in the embryo, in that the fluid in the rudimentary heart and vessels represents a scanty plasma, and the cells suspended in it the primitive blood-corpuscles. At first the latter appear, as has been already mentioned, in the form of plain spherical cells, with finely granular protoplasm, vital contractility, and frequently vesicular nuclei, within Avhich nucleoli may be seen. They 132 MANUAL OF HISTOLOGY. ire still destitute of hemoglobin, which gives them their characteristic peculiarities at a later period of their existence. Their size is also very- various, exceeding frequently that of the cells of fully developed blood. Their average diameter in the embryo of foAvl is, according to my obser- vations, about 0-0128 mm. Little by little the cell becomes clearer, and the characteristic yelloAV tinging Avith haemoglobulin commences, this substance being deve- loped by the body of the former. Such coloured nucleated cells range m their diameter in the human being and in mammals, from 00056 to 0-0160 mm. (Paget, Kblliker). Whilst this transformation of embryonic cells into blood-corpuscles is proceeding with the further development of the circulatory system, the blood must of course contain, at the same time, both kinds of cells, the coloured as well as the more advanced, besides immature colourless ones. During the earlier periods of foetal life, hoAvever, rapid multiplica- tion of the red cells by means of division takes place, as was first observed by Remak. This may easily be folloAved in the embryonic chick. The process begins here Avith division of the nucleolus, then folloAvs that of the nucleus, which generally splits into tAvo portions, and only very seldom, according to Remak, into three or four. Sometimes such a nucleus will divide anew, but it requires a very close search to discover in the chick cells engaged in more than the usual binary division. Finally, the contractile body of the cell is seen to undergo constriction in the middle until the two portions part company. The extreme delicacy of these blood-cells frequently gives rise to artificial appearances, for instance, of cells Avhich are furrowed in the middle, and only contain a nucleus in one-half, or others Avhose two portions containing nuclei are held together by a long, thin, connecting thread. In the foetal chick it is just in these periods of formative life in Avhich the liveliest increase of blood takes place, that this process of division (which may, as it appears, pass over very rapidly) can be best observed. Later on, at a more advanced stage of development, it ceases altogether, according to Remak's and our own observations. We owe much to Kblliker for his profound in- vestigations in regard to the blood of the mam- malia. Of the correctness of his vieAvs I con- vinced myself years ago in embryonic deer (fig. 125), as Avell as later on in rabbits and the human embryo. Here also the same process of division may be recognised. According to Remak, multi- nuclear cells occur also frequently. To me the nuclei always appear granular. Moreover, the act of division is liable to temporary variations, it ap- pears. Thus in rabbit embryos of 9 mm. long I have only remarked a very small number of cells Fig. 125.—Biood-ceiis from the engaged in diAdsion, Avhile the process could be ^rrsSarceiisdaeteia ^ ^recognised in much larger ones. The fur- b1to1/:Plicutionufthesamefl'oin destiny of these in general still larger cells . °; (though they may vary considerably as to dimen- sions) consists m this, that they take on more and more the spherical form l7sanLTrsnTtb ^^ t0+.S,'Ze'.and assume tbe Epical shape; the nucleus disappears at the same time m mammals. Even at a very early period TISSUES OF THE BODY. 133 isolated examples of such fully formed, yet extremely delicate cells may be observed among the spherical and nucleated of a still earlier stage of development. Thus the embryos of the rabbits Avhich I have examined, ci about 9 mm. long, showed £th to ith of the whole number already Avith- out a nucleus, and presenting the characteristic form of the blood-cell. Kblliker found in sheep embryos of S-6 mm. long no such mature blood- corpuscles, and Paget missed them also completely in a human foetus 9 mm. in length. According to the first of these investigators, they are still uncommonly rare in fcetal sheep of 20 mm., A\diile they constitute by far the largest proportion of the cells in the young of the same animal measur- ing 29 mm. In human embryos of the third month they only amount to about from £th to ^th of the Avhole mass of the blood. Sheep embryos, on the other hand, of 11 to 29 mm. sIioav a fall in the number of nucleated cells to a very small fraction. The continued multiplication of red cells, Avhich goes on naturally after the process of division has ceased, appears to he carried forward in the foetus, as in the adult, by the lymphatic glands, the medulla of bones, and by the spleen. Very early the characteristic, lymph-corpuscles, derived from the latter sources, may be seen among the other coloured cells. That the liver takes part in the formation of blood, as has been supposed, appears very doubtful. Hemarks.—Much has been adduced within the last few years in regard to the exit through the walls of vessels of the cellular elements—an occurrence of the highest significance in pathological and physiological questions, and especially in inflamma- tion. 2. Lymph and Chyle. §82. While describing the foregoing tissue we mentioned that certain of the constituents of the blood are constantly passing from the capillary vessels into the surrounding tissues in the form of Avatery solutions. This escape of fluid is indispensable for the nutrition of the various parts of the body, the organs as Avell as tissues, in that in these solu- tions various alimentary materials are contained. Now the latter, we know, are different in the several tissues; they are specially adapted, for instance, to the Avants of bone, of the brain, of muscle, and so on. Then the fluids of the tissues become gradually quite different as to chemical composition by the loss of various materials of nutrition in particular parts of the body. But to these fluids are also added the results of the interchange of matter going on in the tissues; the products of their decomposition; and these are also, as has already been remarked in the chapter on general chemistry, again different in the several organs. Here, then, Ave have a neAV source of variety in constitution of the several tissue-juices of the body. Now for the carrying off of the latter, as far as they do not immedi- ately return to the stream of the blood by processes of diffusion; the body is supplied with a special system of fine canals which communicate by means of their main outlets (already long knoAvn) Avith the circulatory apparatus. Their mode of commencement is only partially understood at present. This system of canals is known as the lymphatic or absorbent system. 134 MANUAL OF HISTOLOGY. and the colourless fluid found in its vessels which has been strained off from the blood-capillaries, as " lymph." Now the latter, although it may appear pretty much the same to the observer's eye in the various regions of the body, cannot possibly have identically the same composition everywhere from Avhat we have just seen above. On the contrary, it will always be found to differ according to the nature of the tissue or organ from Avhich it Aoavs, and to be, there- fore, a fluid of more variable constitution than the streams of blood belonging to the several regions of the circulatory system. There is, hoAvever, in our body one portion of the lymphatic system which serves other purposes, at least, at certain times. The lymphatic canals namely, of the intestinal mucous membrane contain in the fasting state a fluid possessing all the usual characteristics of lymph. During digestion, however, there enters by the radicals of this system of canals a mixture of albuminous substances and fats taken up from the alimentary matters. We now find the passages charged with a whitish, opaque, and frequently milky fluid, toAvhich, owing to its appearance, the name "milk-juice" or "chyle" has been given. These particular vessels are then spoken of as lacteals. ■ § 83. Both these juices contain, suspended in a plasma or fluid intercellular substance, a considerable number of cells all possessing the same nature (lymphoid cells); these are known, from the mode of their occurrence, as lymph and chyle corpuscles. They were first discovered by Leeuwenhoek and Mascagni. In all essential particulars they correspond with the colourless cells of the blood, already discussed at (§ 69); nay more, they are identical Avith them. The cells of the lymph and chyle, namely, pass into the blood, and circulate there as white corpuscles. Besides these, there are other immeasurably small molecules to be seen, especially in the chyle, as also larger elementary granules, while in some particular regions, especially of the lymphatic system, isolated red blood-cells may be observed. The cells in both fluids display much variety as to size and other relations, and no regular laAv seems to govern their distribution, although one or other form of cell may at times gain the ascendancy in this or that region. It is a fact of great interest, further, and one which may be especially clearly recognised in the chyle absorbents, that either none at all, or very feAv of these corpuscles are to be seen in the finest radicals, Avhen on the point of leaving the wall of the intestine; but that they be- come all at once very numerous in the Fig. i26.-cei:s from lymph. Fromito Juid after the passage of the latter through 4 unchanged; at 5 the nucleus and ine mesenteric glands. Ihe same may be envelope appear, also at 6, 7, 8; at obsprved in n+Lov mvf„ ~f i.i,„ i i .• 9 the nucleus commences to divide, UUbeivea m °tner parts ot the lymphatic as also at 10 and 11; at 12 it has sepa- System. rated into six pieces; at 13 we have "NTnur no +^ +!,„ ll xi. i liberated nuclei. imow as to tne cells themselves, more q1 , ., , , particularly, they may be said to have been already considered when speaking of the blood. They are the same for- mations, namely, with like diversity as to size, as to the body of the cell and. its contents, with the same kind of nuclei and endowed with the like vital contractility as the colourless corpuscles of that fluid TISSUES OF THE BODY. 135 But while the cells of lymph and chyle are everywhere alike, the con- trary is the case with the remaining elementary particles of these fluids. On microscopical examination the chyle of mammiferous animals dis- plays a certain amount of turbidity—the cause of its white colour to the eye—produced by innumerable minute dust-like particles suspended in it, and not by small globules of fat with Avhich this fluid Avas formerly sup- posed to be so richly filled. These particles (as is usually the case with substances in a minute state of division suspended in fluid), are engaged in a peculiar tremulous or restless movement, termed the molecular motion of Brown. The more opaque and milky the chyle appears, the more nume- rous are these molecules found to be. They decrease in number again in the larger passages of the lymphatic system, and are completely absent in the clear lymph of fasting animals. Eventually these particles flow from the absorbents into the blood through the ductus thoracicus, and may form in it transient constituents of the plasma. As to ascertaining their magnitude, with any approach to accuracy, we must confess our utter inability to do so, owing to their extreme minuteness. These dust-like molecules consist, Ave are told by H. Muller, of neutral fats enclosed in a Avondrously delicate layer of a coagulated protein substance (albumen). Owing to this they do not coalesce, as free fat globules would do, nor do they on the addition of water. But if chyle be evaporated to dryness, the particles do unite on the subsequent addi- tion of Avater, as also Avhen acetic acid is mixed with the fluid. They are dissolved by ether, to the action of which the albuminous envelope seems to present no obstacle. We will see further on that these fatty particles represent the fats of the food absorbed from the intestinal tract. Besides these, larger and less clearly defined elementary granules of 00002 - 00011 mm. in size are to be found in the chyle, partly scattered and partly in groups. They appear to be the Avreck of lymph corpuscles, and probably occur in the blood also (§ 64) (Hensen, H. Muller). Finally, Ave have blood corpuscles again brought before us in both lymph and chyle. Some of these, doubtless, gain access to our prepara- tions from wounded blood-vessels, and the admixture may be completely avoided by careful dissection. On the other hand, such red cells may be found almost always in the ductus thoracicus of many animals, as, for instance, in that of the dog. The lymph of the spleen further appears to be very rich in red cells (Tho?nsa), as also that of the liver (Hering). From this there would appear to be but little doubt that in isolated casea lymph-corpuscles may undergo transformation into red cells before enter- ing the circulation. For my own part, I believe, I have observed inter- mediate forms in the thoracic duct of the rabbit, between the two species of cells; they are also to be seen in the blood of the splenic vein (§ 76), and in the medulla of bones. On the other hand, the possibility of a migration of red cells from the blood-vessels into the lymphatics through the walls of the former (§ 81), Hering, must be allowed. §84. Now, the question as to the source of these lymph and chyle cells, is one of the utmost importance for the histology of the present day. And since their spontaneous generation in both fluids could not any longer be alloAved, and that they were found to be either entirely absent, or oidy to occur with extreme rarity in the commencement of the absorbents, while immediately after the passage of the fluid through the lymphatic 10 136 MANUAL OF HISTOLOGY. glands they were met with, the possibility of their origin in these so- Sailed glands was recognised even years ago. This view received sup- port, also, from the discovery that the contents of the latter is the same as that of the lymphatic vessels. In the mucous membrane of the digestive tract there occur also small lymphatic glands, known as Beyers patches," and hence the origin of the few isolated lymph-corpuscles found in the smaller branches of the chyle vessels, leaving the intestinal U And, in fact, the cells of lymph and chyle are the corpuscles of these organs which have penetrated into the hollow interstices of the lymph- nodes, and have been carried off by the stream of fluids. These points if borne in mind will render the description of the lymphatic glands more easy of comprehension, in discussing which we shall have to consider the origin of the cells in question in the latter organs. How far these cells are capable of undergoing multiplication in the lymph and chyle streams, is also a matter worthy of our consideration. At present we are in possession of no reliable facts bearing upon this point. . § 85. HoAvever important it might be to determine the amount of these fluids in the body, even approximately, science possesses at present no certain data to go upon in regard to their quantitative analysis. We can only, so far, conjecture that the amount of both must be very considerable, and that, as through the lacteal system, so also through that of the lymphatics, an extensive intermediate circulation exists. If we now turn to the chemical constitution of these two fluids, Ave have at present but very insufficient analyses to go upon. Hitherto it has not been possible to investigate chyle and lymph in a manner adequate to the requirements of histology. We cannot yet even accurately determine the composition of the moist lymph-cell. All the rough analyses, too, which have hitherto been made, display enormous differences, OAving to the difficulty of obtaining large quantities of lymph and chyle in a pure state, and to the changeable nature of both liquids. As to the cells, they consist of various modifications of albuminous compounds, the enveloping layer showing different reactions to those of the nucleus and protoplasm of the body of the cell, which encloses molecules of a coagulated albuminoid, and of fats : it is soluble, namely, in dilute acids, Avhile the nucleus is not. Lymph is a more or less clear, alkaline, watery liquid, whose specific gravity is not yet known. In it may be found, again, those protein sub- stances which are likewise present in the plasma of the blood namely, the two constituents of fibrin, with albumen and its modifications. The • former give rise here, also, to the coagulation of the fluid Avhen collected in a vessel. And yet a difference exists between the fibrin of lymph and that of blood in the manner in which it solidifies. Lymph, namely, does not usually coagulate in the corpse, but subsequently on being drawn off, and only after frequently very long continued exposure to the oxygen of the atmosphere. As far as is known at present, from ten to twenty minutes appear necessary; but even an hour may pass over before it takes place (Nasse). The lymph-clot retains also, as was the case with that of the blood, the form of the vessel in which it solidifies, but is naturally much smaller on account of the much smaller number of cells TISSUES OF THE BODY. 137 Avhich it contains. Another peculiarity frequently observed, and which I myself am in a position to verify, is also very striking; the coagulum, namely, may become red on exposure to the air, a change of colour probably depending upon the generation of the pigmentary principles of the blood through the action of the atmospheric oxygen. The amount of fibrin seems, moreover, to be liable to considerable variation. The albumen of lymph exists, like that of the plasma of the blood, in combination with soda as albuminate of sodium. Casein is missed, as in the blood also. The fatty matters, individually but slightly knoAvn, appear partly as neutral fats and partly saponified Avith soda. Their amount, like that of albumen, seems to vary considerably. Besides these, lymph contains also grape sugar and urea As to the extractives which are here met with in no small amount, their nature has not been investigated. Chloride of sodium is very strongly represented among its mineral constituents, as well as the carbonates of the alkalies; besides which, the usual combinations of phosphorus and sulphuric acid of the system all occur in lymph. • Finally, iron also makes its appearance here. Although the proportion of water in this fluid always remains larger than that in the liquor sanguinis, it is still subject to very considerable variation. Lymph contains no oxygen, or only traces of it; it does, however, possess nitrogen in small amount, and carbonic acid seems to be present in great abundance. A portion of the latter is held in loose combination, another portion can only be displaced by acids. On the Avhole, it would seem that lymph possesses a composition allied to that of the plasma of the blood, both of them apparently con- taining exactly the same proportion of salts (Nasse). But in general it may be stated to be richer in Avater and extractives, but poorer in albumen, fats, and salts than the liquor sanguinis. Not long since analyses Ave re undertaken by C. Schmidt, in which, for the first time, the coagulum and serum of lymph were separately treated. The lymph to be analysed Avas obtained from the neck of a foal, Avhich had been previously Avell fed Avith hay: it showed the folloAving com- position :— 1000 parts of lymph contain Serum, . . . ' . .955-2 Coagulum, . . . .44-8 1000 parts of coagulum contain:— I 1000 parts of serum contain :— Water, . . . 907-3 | Water, . . . 957-6 Fibrin, . . .48-7 Albumen, . . 32-0 Albumen, . . 1 Fats and fatty acids, > 34 3 Other organic matters, ) Salts, . . .'9-7 Fats and fatty acids, . 1-2 Other organic matters, 1 -8 Salts, . . . .7-4 In regard to the mineral constituents, Schmidt observed a similar, though less marked, contrast between cells and plasma, as in the blood (comp. § 75). Now, as to the chemical constitution of the chyle, we find it slightly alkaline. Owing to its greater richness in fatty matters also it is more cloudy or milky than the fluid last mentioned, and in general richer in solid constituents, so that its specific gravity lies between 1*012 and T022. 138 MANUAL 01 HISTOLOGY. It partakes of the same peculiarity as lymph, in coagulating some con- siderable time after it has been collected from the body; it does so, how- ever, with much greater rapidity on the addition of a certain amount of blood (A. Schmidt). We have already mentioned (§ 11) that the fibrino- gen of the latter fluid has its origin in the red blood-corpuscles. Ihe coagulum of chyle may also subsequently become red on exposure to the air. Its fibrin generally contracts much less, and remains more gelatinous, at the same time that it possesses greater solubility. Albumen, an important constituent, as we would be led to expect from the nature of chyle, appears in considerable, but, according to the kind, of food, variable quantity. We have already mentioned its partly forming the envelopes on the minute molecules of this fluid; but another portion of it is present in the form of solution* in water. The amount of fats, also, in chyle, though necessarily subject to great rise and fall, is far larger than in lymph. Primarily, whilst in the finest vessels all of them are found as neutral compounds suspended in a state of the most, minute division, later on saponified fats make their appear- ance, as observation with the microscope teaches us, by means of Avhich we see the formation of fat-globules in a clear fluid on the addition of an acid (H. Muller). Again, we find that grape sugar and urea are contained in this fluid. It may also have lactic acids in its composition, according to Lehmann. Chyle contains, also, a by no means inconsiderable proportion of ex- tractive matters and the ordinary mineral compounds, such as the alkaline salts, with chloride of sodium in large quantity. Further, minute quantities of the earthy salts and iron have been found in it. A rather old analysis of Rees (1) may serve as a clue to the com- position of the chyle, beside which we give one of lymph by the same author. seven hours after having beer Rees). fed on peas and beans (after From the extremities of the same animal. Water, 902-37 965-36 Fibrin, 3-70 1-20 Albumen, . 35-16 12-00 . Watery extract, 12-33 1319 Alcoholic do., . 3-32 2-40 Fats,. 36-01 Traces Salts, 7-11 5-85 Strangely enough, the most recent experimenter on chyle, C. Schmidt, arrived at completely different results in his analysis of that from the thoracic duct of the foal. According to this observer, the composition of both fluids, of lymph and chyle is exceedingly' similar, except that the latter showed a somewhat larger proportion of iron, whilst the amount of fat found in it was extremely small. The following is the composition of the chyle obtained from the thoracic duct of a healthy foal, which had been fed three hours before with meal-pap and hay :— 1000 parts contained Serum, Coagulum .... . 967-4 32-6 TISSUES OF THE BODY. 139 In 1000 of coagulum of the chyle :— Water, . . .887-6 Fibrin, . . .39 0 Free fat, . . . 1'5 Fatty acids of the soaps, 0-3 Albumen . . . "1 Sugar and other organic >■ 66-0 matters, . . ) Haematin, . . 2-1 Mineral constituents without iron, 5-5 In 1000 of serum of ditto :— Water, . . . 958-5 Fibrin, Free fat, . Fatty acids of the soaps. Albumen, Sugar and other organic ) matters, . . j Haematin, Mineral constituents ) without iron, . j 0-5 0-3 30-9 2-3 7-5 As yet we knoAv but little as to the first appearance of lymph-cells in the embryo. But from the fact alone, that lymph-corpuscles may be observed in foetal blood at an early period, we may infer that they occur also largely in the lymph. Remarks.—London, Edinburgh, and Dtoblin Philosophical Magazine, Feb. 1841. Comp. also Nasse's article "Chyle," p. 235. B. Tissues composed of simple cells, with a small amount of solid intermediate substance. 3. Epithelium. §86. By epithelium we understand a tissue formed of closely associated cells, which clothes, in layers of greater or less thickness, the external and internal surface of the body, canals of exit and even numerous com- pletely closed cavities of the system. It is only through the nearer acquaintance with the history of its development that we have been enlightened as to its true nature. And for this we are indebted to the searching investigations of Remak, from which we learn that at an early period of development the flat rudimentary embryo is bounded above and beloAv by two strata of cells, the corneous and intestinal glandular layers. From the first of these the epithelium of the external surface takes its origin, and from the second that of the digestive tract. But the cells of these two layers play a further part in the construction of numerous other organs. Thus Ave find that it is not alone the outer clothing of the body, the skin, Avith its manifold reduplications, which bears these epithelial layers of cells, but the mucous membrane also Avith which it is continuous, the glands of the intestinal tube, the internal surfaces of the respiratory and generative apparatus, and even parts which have completely ceased to communicate Avith these primordial epithelial layers; as, for instance, the cavities in the brain, the spaces and hounding surfaces in the eye and auditory organs: these all possess this characteristic covering. Owing to the fact that the secreting gland-cells having the same origin as the epithelia, Ave frequently find transitions from one kind of cell into the other in the interior of those organs. The epithelium extends, hoAvever, still further throughout the body. The strata of cells enclosed between the corneous and intestinal glandular layers, namely, the so-called middle or intermediate layer, becomes, with 140 MANUAL OF HISTOLOGY. Fig. 127.—Flat epithelium cells from the human mouth. advancing deA'elopment, the seat of various cavities Avhich acquire subse- quently on their inner surface a clothing of epithelium. It is in this exceptional manner that the epithelia of serous cavities and lining mem- branes of the heart, Avith the blood and lymphatic vessels, have had their origin. The elements of epithelium are pale, transparent cells, Avith distinct nuclei, only absent in the older cells of many kinds of tissues. The size of these cells is liable to vary greatly; it lies betAveen 0'0074 and 0-056 mm. ; that of the nucleus is less so, whose diameter may be stated on an average to be from 0-0045 to 0*0091 mm. The appearance of the latter may be vesicular, homogenous, or granular. It has already been remarked that the surfaces of the body are clothed Avith layers of epithelium of varying thickness. The depth of the tissue, in fact, changes to a most extraordinary extent in the several localities of the system. AVhilst some strata of epithelial cells may attain a height of 2 mm. and upwards upon the external skin of the human body, so that they Avere recognisable to earlier generations of anatomists without the aid of the microscope, they may yet decrease in thickness in other places, forming thin coat- ings of only a few layers of cells, invisible to the unaided eye. Finally (and this is the case over by far the greatest portion of the sur- face of the body), this tissue may consist of one single extremely delicate layer of cells. The most important feature Avhich this so widely-distributed tissue presents for our consideration is the variety of form Avhich it displays, Avhich has led to the recog- nition of several distinct species of epithelium. It is comparatively seldom—and in the human body over very limited areas—that epithelial cells preserve, the original typical form of the cell, namely, the sphe- roidal. We generally find either one or other of the changes affecting the spherical body already considered (§ 46), i. e., flattening or lateral compression, so that it usually appears, Avith modifications in particular instances, either as a flattened, squamous, or narrow cylindrical cell. We must therefore distinguish between 1, the flattened or pavement epithelium (fig. 127) and 2, cylinder or columnar epithelium (fig. 128). Other modifications of this tissue may arise from the free surface of the cells bearing minute hair-like appendages, as Ave have already mentioned. Thus a third special form is produced, the ciliary epi- thelium, fig. 129. In man and the higher animals it is almost exclusively upon the cylindrical cells that these supplemental structures occur. Again, in certain regions of the body the cell is found to possess peculiar contents, namely, granules of black pigment or melanin, with which its body may be chared In human beings and mammalia it is only the more flattened cells of the epidermis which have these exceptional contents. Thev represent what used to be described by histologists as polyhedral pJgmZcdll Fig. 128.—Cylinder or columnar epithelium from the large intes- tine of the rabbit. Fig. 129.—Ararlous forms of ciliary cells from verte- brata. TISSUES OF THE BODY. 141 (fig. 130). According to our way of thinking they should be called pigmentary epithelia. The extremely variable depth of this tissue just mentioned leads to further variety. Besides epithelium, in which many layers are placed one over the other, forming a heavy coating (fig. 131), Ave find others made up of but one single stratum of cells (fig. 132) ; and between the den-vly laminated and non-laminated species there exist many intermediate forms, in Avhich only a feAv strata are to be seen, disposed one over the other. It must be borne in mind, from this Fig. 130—Pigmentary flattened on, that it is only the flattened epithelia which are \?e%a\ 'pigment Scens)%fP°the capable of becoming laminated to any remarkable sheep. extent; but that they need not necessarily everywhere take on this form. §87. The most widely distributed variety of the tissue under consideration is the flattened or pavement epithelium. Overlooking its more limited occurrence in certain regions, it is met Avith on the external skin, on many mucous mem- branes, in serous sacs (true and false), as well as on the internal surfaces of the vessels of the circulatory system. Its thickness is subject to the greatest varia- tion, so that, at one time strongly lamin- ated, it represents the strongest of all epithelia; at another it displays merely a delicate coatirg of cells of the simplest kind. Simple, pavement epithelium (1), in the first place, forms the internal coating of the cavities of the heart, as also of the blood and lymphatic vessels. (2.) It makes its appearance, further, in the true serous sacs on synovial membranes (burste, sheaths, and capsules for the joints). (3.) Again, Avithin the eye, on the posterior surface of the cornea and anterior of the iris ; on the internal surface of the anterior segment of the capsule of the lens ; within the auditory apparatus, namely, on the periosteum of the internal ear, the inner surface of the semicircular canals and vesti- bule. To Avhat extent gland ducts possess such a lining need not for the present be discussed. We find sometimes a simple and sometimes slightly laminated pavement epithelium in the canals of exit of the sweat and ceruminous glands. The infundibuli of the lung are likewise lined by the same species of cell. (4.) Finally, the greater part of the ventricles of the brain in the adult is covered with a species of pavement epithelium instead of the ciliated cells of early life. Fig. 131—Vertical section of the skin of a negro. Thick laminated epithelium lying on the elongated papilla of the dermal tissue (a), with younger cells at b and c, older at d. Fig. 132.—Simple coating of cylinder epithelium on a mucous membrane. Fibrous tissue of mucous membrane at d; cells at a. 142 MANUAL OF HISTOLOGY. frequently dust-like molecules. The elements of this tissue consist of pale flat cells (fig. 133) placed closely together, and without any apparent intercellular matter. 1 ney are frequently destitute of granular contents, but display at times very minute Such is the indistinctness of limitation in the cells, in certain instances, that their outlines may not be apparent, or they may seem to fuse into one an- other. Their boundaries usually become visible, hoAvever, in the form of dark lines, on treat- ment with a dilute solution of nitrate of silver. These cells possess distinct nuclei, sometimes granular, sometimes smooth-edged, in the in- terior of which one or more nucleoli are usually Fig. 133.—simple pavement epi- visible Their form is tAVofold; in one instance ^.SSTSSTuSAi they may be broad, with a polyhedral outline view. (^ anci diameter of 0-0226-0-0090 mm., while the round nucleus is 0-0075-0-0057 mm.; in another their shape is more or less lanceolate, and length—0-0226-0 0455 mm.—with a similarly nar- rowed nucleus (b). In side viev? such cells may present a very peculiar appearance (b); they then seem to possess the form of short fibres, thickened considerably in the middle, where the nucleus is situated. The first of these species of cells is found lining serous sacs, the latter clothing the internal surface of blood-vessels and lymphatics; but here again there exists much variety (Legros). In the arteries Ave find long and narroAv cells, whde the endothelium of veins is made up of shorter and broader elements. The thickness of these structures, and with it that of the whole covering, must, as we have already mentioned, present much variety. Where but a small amount of flattening has taken place, the depth of the cell and thickness of the Avhole layer is generally about 0 0055 mm. and upwards, Avhilst strata Avhich have undergone more compression may sink in depth to only 0-0037-0-0032 mm. Those tall cells, again, which occur in the holloavs of the brain also deserve special notice as peculiar elements; also those of the choroid plexus. The latter (fig. 134) are likewise thicker and rounder, giving off one or more pointed processes, and containing, besides the nucleus, as a rule, one or several granules of a dark brown substance, Avhich is, moreover, absent in the younger cells. Pavement epithelia are very delicate structures Avhich undergo rapid decay in the dead body. In the living subject, on the other hand, they probably con- stitute more durable tissues, with but little power of rapid regeneration however. The epithelia of the lung are perhaps an exception in this respect. The mode of their regeneration is not yet known. Remarks.—1. See Henle's Allg. Anat. p. 226, &c. Luschka, Die Structur der serosen Haute. Tubingen, 1851. 2. We refer our readers to the special chapter on the vas- cular system for the rest. 3. Those views which were formerly entertained on this point, and which taught of the existence of a laminated pavement epithelium on the surface of connective tissue, Avere based on deceptive appearances. However, at an early embryonic period the surfaces of cartilages do seem to be clothed with a layer of cells similar to those of epithelium. We will refer to this again. 4. Comp the paragraph on the respiratory apparatus for the epithelium in question. Fig. 134.—Epithelial cells from the hu- man choroid plexus, a, cells from above; 6 and c, side views of the same. TISSUES OF THE BODY. 143 §88. The simple pavement epithelia just referred to pass, without any sharp line of demarcation, into the more or less strongly laminated species, through certain intermediate forms. Thus, on the internal surface of the tympanum and dura mater, and external surface of soft skin, Ave find an epithelium formed of several layers, but still thin; of these the more superficial are recog- nised as formed of larger and flatter cells. The anterior surface of the cornea of mammals affords an interesting example of a moderately laminated epithelium. Here Ave find from seven to nine layers of cells laid one over the other. The counting of them, however, is not in all cases easy. In some of the strata Ave observe flattened cells, and in others call bodies, generally of round figure, but often assuming other forms under the influence of lateral pressure. The undermost layer consists of naked elements, greater in height than in breadth, and having each a full, plump nucleus (perpendicularly elongated cells). The lining of the urinary apparatus is still less markedly laminated. The uppermost layer is formed of a single stratum of cells of different sizes, with vesicular nuclei. Their under surface displays a varying number of grooves Avith ridges and prominences situated between them. Applied to these depressions, we find the rounded ends of columnar cells belonging to a second layer. Then follows a third stratum of more irregularly shaped elements, at one time cylindrical, at another, more or less fusiform, next to Avhich, finally, a fourth and terminating layer of small polygonal cells may be recognised (Linck, Henle). The pavement epithelium of many mucous mem- branes of the body often displays much stronger and even very considerable lamination, as for instance, that of the conjunctiva of the eye, the entrance to the nares, the cavity of the mouth and pharynx, as Avell as the oesophagus doAvn to its connection with the stomach, the vocal cords, and finally, the mucosa of the female genitals, as far up as the uterus. For a closer examination of these typical formations, the mouth may be recommended as peculiarly adapted (fig. 135). In the deepest layers, seated immediately upon the fibrous tissue of the mucous membrane, Ave meet with strata of soft small cells of roundish, or at times more oval figure, with a diameter of only about 0-0075 or 00114 mm., and vesicular Fig.—135.—A papilla from the gum of a child, showing the vascular net-work and lamination of the epithelium. *%ifiw^ ^rfy$ Fig. 136.—The so-called spinous or furrowed cells. At a, from the undermost layers of the human epi- dermis ; at 6, from a pa- pillary tumour of the human tongue. 144 MANUAL OF HISTOLOGY. nuclei of 0-0056 mm. in size, or less. All these cells display under high microscopic powers a very peculiar structure (fig. 136). Their Avhole surface namely is covered with prominent ridges and spines (a), by mean of which neighbouring cells are attached to one another, " like two brushes whose bristles are pressed in among one another " (Schultze). In the outer layers, finally, the epithelial cells (fig. 136) appear as thin scaly structures, without either grooves or pro- minences, and of considerable size (0*0425- 0-0750 mm.), with more or less oval and homogeneous nuclei of from 0-0090 to 0'0114 mm. Here the body of the cell con- tains a few granules usually in the vicinity of the nucleus. But the cell has also changed in its physical condition. Instead of the softness of former days, it now manifests a greater Fig. 137.—Epithelial cells from the , , .ri_i jv -i-ii uppermost layers of the human or less degree of hardness and _ brittleness; moutn- it has become horny, as the saying is : it is also destitute of soft protoplasm. Apart from the differences in thickness which the whole bed may show (being, according to Henle, 0-2 mm. on the palate, and on the gums, behind the teeth, betAveen the papillae, 0*4 mm.), the cells of the locality just mentioned seem to differ but slightly. The persistence of epithelium, already considered in speaking of the simplest pavement cells of closed cavities, appears to be the same in the urinary apparatus ; in the thickly laminated coatings of other mucosae it is well knoAvn not to obtain. Here we have to do with a tissue under- going rapid repair, in that a certain quantity of the most superficial cells is rubbed off continually, forming a regular constituent of the mucus of the part, Avhilst the deeper cells advance to the surface, and a process of cell-formation takes place in the undermost strata in order to cover the loss of the desquamating cells of the surface. The multinuclear epithelial cells which may be observed, by no means unfrequently, in deep parts of the strata, are evidence in favour of such a process of cell-formation, That the obliteration of the spines and ridges in senescent cells prepares them for separation, is very probable. Remarks.—M. Schultze in Virchow's Archiv, bd. 30, s. 260. §89. A modification of the pavement epithelia we have just been discussinc is found in the eye, in the so-called "polyhedral pigment cells" of the uvea These are epithelial cells, partly laminated to a small extent, and partly not, and moderately flattened, which occur in the eye in the form of a delicate mosaic. They have peculiar contents as a rule, made up of numerous elementary granules of the black colouring matter, melanin already described (p. 52). These cells are met Avith on the internal surface of the choroidea in an unbroken but single layer, which becomes suddenly laminated in the vicinity of the ora serrata of the retina, at the same time that the individual elements decrease in size. Thus arranged, they are found covering the ciliary processes, and in the human eye the posterior surface of the iris as far as the edge of the pupil. The granides of black pigment are sometimes elongated, sometimes TISSUES OF THE BODY. 145 rounded, and usually appear darker the smaller they are, in any one individual. They are probably crystalline. The tint of the mole- cules is by no means exactly the same in different mammals. In man, where the granules are small, it is seen to be brownish black, but in many of our mammalia, as in the pig and calf, it is jet black. The size of these particles remains always considerably below 0-0023 mm. Answering to their minuteness, they sIioav, on becoming free in Avater, the liveliest molecular motion, a phenomenon Avhich may, however, be remarked in the substance of uninjured cells Avhen strongly swollen under the action of imbibed Avater. The pigmentary epithelium itself (fig. 138) appears on the choroid as a simple bed of closely crowded cells, of a beautiful polyhedral, usually hexagonal figure, running at times through whole groups (a) with the greatest regularity. And yet they may be found indefinitely angular; and some unusually large cells are frequently octagonal (b). The diameter of most of these cells is on an average 0-0014-0*0201 mm., and their thick- ness 0-0090 mm. The quantity of molecules of melanin contained in the transparent thick and tenacious contents of the cell is by no means everyAvhere the same. We meet some cells (and they are the most suitable for examination) in Avhich the amount of black elementary particles is but small, so that the nuclei and mem- branes, always very delicate, may easily be distinguished. In such specimens the nucleus is found to be 0-0055-0-0075 mm. in size, either round or more or less oval, and always smooth-edged. It has usually one or more nucleoli. But much oftener the amount of molecules in the pig- ment cells is far more considerable, so that the nucleus only glistens through as a clear speck. Should the particles remain somewhat distant from the external surface of the cell-body, such groups of cells appear at first sight as though separated by narroAv intervals of transparent inter- cellular substance. Finally, cells are encountered, a in Avhich, such is their richness in pigmentary par- ticles, the nucleus is completely hidden. A side view of these pigment cells (easily obtainable, owing to the small amount of flatten- ing present in the structure) shoAvs that only in one-half of them, namely, that directed towards the retina, do these melanin granules occur, a transparent contents occupying the other half. The nucleus is situated in the latter, or at the 1 unction of the clear and dark portions (fig. 139, b). In conclusion, we may remark that c#lls with two nuclei are also encountered here, but are of rare occurrence. At the boundaries of the choroid, near the processus ciliares, the lami- nated cells are smaller and less clearly polygonal, while they have become far richer in pigment, so that the nucleus can only be rendered visible in general by squeezing the cell-body. The lining of the back of the iris is of precisely similar nature. Fig. 138.—So-called pigment cells from the choroidea of sheep. At a, a mosaic of hexagonal cells; at 6, a larger octagonal. Flg.139.—Cells from the choroid of the calf, a, cell with two nuclei; 6, a side view of ordi- nary cells, moderately filled with pigment; c, some which are only supplied with but a scanty amount of pigment particles; from the neighbour- hood of the tapetum. 146 MANUAL OF HISTOLOGY. With those mammals in which the choroidea forms a tapetum the epithelial cells of the same undergo an interesting modification being here destitute of the pigment molecules of the contents. On the bound- aries may be found certain intermediate forms, with very scanty colouring matter (fi" 139, cd); besides which some isolated black cells are encoun- tered among the colourless ones of the tapetum. In albinos, where the pigment fails completely in the eye, all these cells with which we are now engaged are completely bleached, appearing in the form of a very delicate pavement epithelium. This interesting fact may be verified on any white rabbit. The more markedly laminated epithelia have no pigment cells in man, but such may make their appearance in other mammals, as, for instance, in the conjunctivas of the horse (Bruch). Remarks.—1. This layer of cells belongs, however, as we learn from the history of development, not to the Uvea, but to the Retina. §90. The region in which pavement epithelium is most strongly laminated, though indeed with certain modifications, is the external surface of the body. The surface of the cutis, which appears quite smooth to the unaided eye, is covered, neArertheless, by a number of minute prominences known as the papillae tactus (fig. 140, a, a, a). These, together with the depres- sions between them, are covered Avith very numerous layers of cells lying one over another (b c d). Of course, the latter naturally possess a far greater depth in the intervals betAveen the papillae than on the apices of the latter, in that the surface of all the strata collectively, or the epidermis, is tolerably even. But apart from, these inequalities, produced by the ridges of the cutis, the thickness of the Avhole clothing of cells is very different in the various parts of the body. It may range from 0-04-3 mm. and upAvards, the more superficial layers of flattened cells being subject to the greatest change, the deeper, smaller, and rounder, to least of all (C. Krause). The unequal pressure Avhich the various portions of the skin experience, differences of occupation, and consequent use of certain parts of the body, especially of the hands and feet, account, at least in a great measure, for this. And yet it has long been known that the epidermis on the sole of the foot, even in the foetus, is much thicker than that of any other region of the body. The cuticle of human beings and other mammalia may be divided into two groups of strata, into a superficial and a deep, Avhich are continuous with one another, at one time gradually, at another Avith a tolerably sharp line of demarcation. The first (d) is usually termed the epidermis in the more precise meaning of the word, while the second has received the name of the Malpighian layer, or rete mucosum (b, c). By a certain amount of maceration, these »may be separated from one another. From the fact that the deeper strata fill up the intervals between the papillae, they must naturally possess here quite a different depth from that the points of the latter, as already mentioned. Hence their appearance is rendered more or less sieve-like or reticulated, Avhich has given rise to the name generally employed by the older anatomists. In these deepest layers Ave encounter not free nuclei, but small cells of about 0 0075-0-0090 mm. in size, of roundish or oval form, in Avhich case TISSUES OF THE BODY. 147 The outlines of ; they contain a Fig. 140.—Skin from a negro's leg. At a, the papillae of the cutis, upon which the cells of the epidermal layers may be observed ; d, older, and b and c younger, strata. their diameter is greater, and may rise to 0-0114 mm. these cells are very delicate and difficult to distinguish more or less granular, and frequently yelloAV nucleus, 0-0045-0-0075 mm. in diameter, Avhose shape is either roundish or oval. Then there follow a consider- able number of strata of cells lying one over the other, in Avhich, however, the latter become gradually larger, ranging from 0-0181 to 00280 mm. A poly- hedral flattening is apparent at the same time, and the cells seem to increase in superficial extent, their nuclei becoming paler and assuming more of a lenticular form. All these layers of the rete Mal- pighiicontainthe same spinous and ridged cells already described as occurring in strongly laminated mucous epithelium (fig. 141 a). But besides these younger epithelial elements, lymphoid cells Avhich have wandered out of the blood-vessels are encountered in varying frequency (§ 81). They may be distinguished by their brilliant border, irregular outlines, and very small size. Finally, Ave come to the smooth-edged cells of the horny or outermost layers, or epidermis in the more restricted meaning of the word, whose diameter is 0-0285-00450 mm. From beloAv upwards they become more and more like flattened scales, formed of a transparent and solid substance, without any immediately recognisable membrane (fig. 142). Though in this respect they resemble the most superficial cells of lami- nated mucous epithelia, they still differ from these in possessing no nuclei. This absence of a nucleus is, however, immaterial, for in young embryos all, even the most superficial scales, are nucleated, as also those on the adult body, at spots Avhere the skin is of a soft texture, and naturally moist. Xoav, as the layers of the epidermis lying one over the other present a dull white or brownish appear- ance, they must, more or less, damp the deep red colour, due to its great vascularity, ofthe cutis lying underneath, and, moreover, in a degree proportionate to their thickness. We are taught this also by experience. In those localities, namely, Avhere the tint of. the skin is reddest, the epidermis is very thin, as on the lips and cheeks. It attains, on the contrary, in the sole of the foot and, with many individuals, in the palm of the hand, a great thickness, combined with a progressive decrease in the red flesh colour, until at last at those points Avhere the cuticle is thickest nothing but the tinge of the epidermal layers is apparent. This is also seen in Aveals. It is Avell knoAvn that the skin of Europeans presents at certain points a brownish tint, lighter in blonde individuals than in brunettes. Among Fig. 141.—So-called spinous or ridged cells, o, from the deeper layers of hu- man epidermis; 6, cells from a papillary tumoui of the human tongue. 148 MANUAL OF HISTOLOGY. Fig. 142.—Cells from the human epidermis, a, from above; b, cell with a globule of fat lying upon it; c, another in half profile. these points may be reckoned the nipple and areola of the breast, the scrotum, the labia, and the vicinity of the anus, as well as the more indi- vidual cases of freckles and moles. iNoav, this colouring, Avhich is only found in isolated portions of the bodies of those belonging to the white human races, appears most exten- sively in the multifarious shades of skin of the remaining varieties of our species, down to the deep black of many tribes of negroes. As far as has hitherto been ascertained, these darker tints (in which the fibrous tissue of the cutis is never affected) are dependent on three conditions, which are combined in the specially marked cases : namely, on a tinging of the nucleus with a usually diffuse pigment; secondly, on a similar but much slighter colouring of the whole con- tents of the cell; and finally, on the deposit in the body of the cell of a granular pigmentary matter. It is principally the deeper layers of the cuticle Avhich take part in these changes (fig. 138 b c). Like the mucous membranes, epidermis suffers considerable loss by desquamation, OAving to friction, Avashing, the pressure of clothes, &c, so that it may be looked upon as a rather transient tissue. Remarks.—When these tints of the skin are less intense, Ave usually find that it is merely the deepest and most recently formed layers of cells which contain nuclei of a slightly brownish colour. But if the hue of the skin deepens, that of the nuclei be- comes intensified to a chestnut brown or brown black. The contents, hoAvever, of the cell are now no longer free, but slightly tinged Avith brown. Finally, in the undermost layers ofthe cuticle wc find cells with granular colouring matter also, which vary in shade from yellow to brown, or even from this to the black of melanin. Here, then, we have epidermal cells containing melanin also in the human subject. §91. We noAV turn to another form of the tissue we are engaged in consider- ing, knoAvn as cylinder or columnar epithelium, occurring in the human body on its mucous membranes. This is the epithelium ofthe digestive tract, Avhose internal surface is clothed by it from the cardiac end of the stomach to the anus in uninterrupted course, Avhere it terminates Avith a sharp line of demarcation against the epidermis. Further, it is found in the larger excre- tory ducts of those glands pouring their secretions into the intestinal tube, as, for instance, those of the pancreas of the liver and gall-bladder. The passages of exit likeAvise, from the mamma and lachrymal glands, as wellas certain portions of the generative system, are lined Avith the same cells. Further, a modified cylinder-epithelium is found on isolated portions of the organs of sense, as, for instance, on the regio olfactoria of the nose, and on the broad papilla of the frog's tongue. We shall have to refer to this again. This species of epithelium consists of a single layer or coating of tall narroAv cells, set up perpendicularly on their ends, Avhich either possess the same breadth through- out, or are broadest at their free extremities (fig. 143), Avhile at the opposite end they are narroAved down more or less to a point. In many of these cells the nucleus lies about in the middle, in others it is situated lower down. Externally, we find here also a polyhedral accommodation where the cells come into contact, so that cylinder epithelium, observed from above, often presents the appear- Fig. 143. —Cylinder epithelium from the large intestine of the .rabbit; in pro- file. TISSUES OF THE BODY. • 149 Fig. 144—Cylinder cells of a mucous membrane, arranged perpendicularly (diagram- matic), a, the cells; b, the intermediate matter; c, base- ment layer; d, the fibrous tissue of the mucous mem- brane. ance of an extremely delicate mosaic, similar to that of pavement epithe- lium. But the fields are smaller, and the nuclei lie deeper than the edges of the cell. Below, the pointed portions of the cell, separate at times from one another (fig. 144), in Avhich case the transparent intercellular-substance becomes visible Avith considerable distinctness (b). But where the cells remain broad below, or serve to clothe strongly curved surfaces (fig. 145), they lie in contact with one another throughout their whole length. The nuclei of cylinder cells are roundish and smooth, supplied also Avith nucleoli. The body of the cell is seldom quite transparent, but usually delicately granular and slightly clouded. The membrane is generally very thin and fine laterally, and is probably absent on certain portions of the free base of the cell, or rather replaced by a soft boundary layer ; at times, hoAvever, it is met Avith apparently thickened by a transparent layer of the cell-contents lying beneath it, containing no ganules (fig. 143). Both as to size and form, our cells are subject to numerous variations. Many appear tolerably short, Avhile others are long, and at times also run out into long pro- cesses below. Many of them again are broad, so that the nucleus may be seen surrounded by the membrane at no inconsiderable distance (fig. 143), whilst others remain much narrower. In the latter case the envelope surrounds the nucleus closely, or appears bulged out by the latter. Finally, Ave meet with cells which con- tain double nuclei. The relation of length to breadth in the cells of the human small intestine, is as 0-0182- 00270 mm. to 0-0057-0-0090 mm. at its upper end, while at the openings of the biliary and pancreatic ducts the cells are narrower, with the same length. Henle has seen unusually slender ones in the human stomach. §92. Fig. 145.—An intestinal villus clothed with cylinder cells. a, cylinder epithelium with border; 6, vascular network; c, longitudinal bundles of muscular fibres; d, chyle vessel in the centre. As has already been remarked in the general section (§ 50), cylinder-cells may display strange deviations from the characters just mentioned, especially those in the small intestine of man and other mammals. The thickness of the border pierced with minute pores (fig. 146 a, 147) is, in the rabbit, from 00017 to 0*0025 mm., and the number of lines crossing it from 10 to 15. This secretion of the cell consists, as Ave have already mentioned, of a coagulated protein substance, differing from the membrane, and offer- ing but small resistance to the action of water, on the application of Avhich transparent drops rapidly well from it. Whether these pores 150 « MANUAL OF HISTOLOGY. Fig. 14G. — Cylinder - epithelium from the small intestine of the rabbit, a,, the cells in profile, with the thickened border some- what elevated and traversed by pores; b, view of the same from above, in which the orifices of the little canals appear as dots. really pass through a regular cell-membrane or no has not yet been ascertained. Cells Avhich have puffed out under the action of Avater show clearly the presence of a lateral membrane at least. However, it is not alone the cylinder cells of the small intestine, but also those of the gall-bladder and larger biliary ducts, which possess these thickened lids per- forated by canaliculi ( Virchow, Friedreich); the same structures are said to have been encoun- tered in the large intestine and other localities. Columnar cells containing melanin have neither been met Avith in man nor any other mammal. Cylinder epithelium appears to undergo in general but moderate physiological reno- vation. The older views, according to Avhich a frequently repeated stripping of larger surfaces took place, have long since been recognised as erroneous. Among these cylinder cells, but also between the elements of cdiary epithelia and the soft slimy epidermis of the lower vertebrates, are to be found certain peculiar elements which haA^e been named "goblet-cells" (Becherzellen) (fig. 148 a). They are sometimes dis- posed Avithout order, but at other times possess a certain regularity of arrangement. They have usually the form either of a plump, or more or less slender flask or Avide-mouthed goblet, and are destitute of membrane on their free surface. The nucjeus and protoplasm of these elements is displaced toAvards the loAver pointed extremity, Avhile the other half is occupied by a slimy substance, granular when in a fresh condition, but transparent in speci- mens subjected to maceration. We look upon them as decaying cells engaged in a process of slimy metamorphosis. ° obSa^om^^ =V^ t0™ might almost say, a superabundance of treat es ThiTi,ll 7 ^' °™ acriticisim of those works, but it may be oCveH tW ti, P jJ° e"ter "P°n three different points of ViewC 1 Gobi J^„7e*tha* *h7 "«?«* *te matter from slimy metamorphosis. 2. They "are independentf™P r ^ ^T?8 CngaSed in ordinary epithelial cells. 3. They do nofex sin Zv°™' l°\ derivfd fr0m the artificial productions J> 3 * m the lmnS body> and we purely §93. We turn noAv to the last modification nf t-bic „i,^i.- in «**« epithelium. We uudetttd % ^^^Z^Z^ these are the eilia. The fu% ^mX^U^IT^ Fig. 147.—The same cells. At a, the border has been loosened by the action of water and slight pressure; 6 view of the cells in the normal condition; c, a part of the thickened border is destroyed; d e f, the latter'resolves itself into separate columnar or prismatic pieces. TISSUES OF THE BODY. 151 Fig. 148.—Gobiet-ceUs from the epi- thelium of an intestinal villus from the human subject, treated with Afuller'a fluid (Schulze). a, goblet- cells; b, cylinder-cells. in the form of a cylinder, less frequently as a more rounded or flattened body. The undeveloped elements, lying deeper doAvn in the tissue spoken of as laminated ciliary epithelium, are a rounder, and destitute naturally of the char- acteristic cilia. The columnar cells of ciliated epithelium (fig. 149) manifest the same diversity of form, and the same difference of length, as those of the simple tissue. The free edge of the cell sometimes presents a darker con- tour than the side Avails. Its substance is at one time transparent, at another, finely granular, but ahvays tolerably pale. The number of cilia, as we have already mentioned, is liable to vary, and ranges, probably, betAveen ten and thirty. In mammalian animals and man the cilia appear somewhat flattened, and termiaate above slightly blunted, although some observers speak of their being pointed. The size of these minute hairs is subject to variation among the higher animals. In the first place, those attached to any one cell are not necessarily all of the same length; and again they are met Avith of larger or smaller proportions in different localities. The gigantic magnitude which they attain in many of the lower groups of animals is never seen here. The largest cilia, of from 0-0226 to 0-0340 mm., are found in the human subject upon very large-sized cylinders, mea- suring 0 0445-0-0560 mm., which clothe the upper part of the passage of the epididymis (Kblliker). In other situations the cilia are smaller, as for instance in the coni vascidosi of the testicle (0-0114 mm.), but their length is still less in the epithelial cells of the respiratory organs, namely, 0-0056-00038 mm. The length of the cells themselves ranges in the human body from 0-0285 to 0-0570 mm. The cilia are of a delicate and perishable nature, and consequently decay rapidly a feAV hours after death. At times, however, they remain exceptionally in a very perfect condition even for days in the bodies of the warm-blooded animals. Ciliated epithelium is found in the following parts of the human body:— It clothes the mucous membrane of the respiratory tract, commencing at the base of the epiglottis, after Avhich it covers the whole larynx, with the exception of the vocal chords. Here it is slightly laminated, forming a bed of from 0-0056 to 0-0992 mm. in depth. It likewise extends over the trachea and bronchi with decreasing lamination, until at last the very smallest tubes are covered with a single layer of minute elongated ciliated cells, 0-0135 mm. high (Koelliker). The organs of smell also possess a laminated ciliated epithelium, com- mencing about at that point at Avhich the cartilaginous nose terminates. It is from 0-0451 to 0-0992 mm. in thickness. The regio olfactoria alone, in the more restricted application of the term, is an exception to this with its epithelium, Avhich will be considered more at length in discussing the apparatus. Moreover, it is not only the main cavities which are lined with these cells, but the adjacent ones also connected Avith the organ. 11 Fig. 149.—Ciliated cells from the mammal, a b, simple forms; c, narrow elongated cell; d, one still more so, with double nucleus. 152 MANUAL OF HISTOLOGY. Simple ciliated cells are also met Avith covering the mucous membrane of the female generative apparatus from about the middle of the neck of the uterus up to the free edge of the fimbria. Again, in the male, the oasa efferentia, coni vasculosi, and the passage of the epididymis, down to about its middle, are clothed Avith similar cells, which become larger and support longer cilia as Ave advance downAA'ard (Becker, Kblliker). In the neAv-born child it Avould appear the cavities of the brain and spinal cord still possess throughout a lining of ciliated cells. This is only partially the case, hoAvever, in the adult. Thus, we find these cells in the central canal of the cord, at the posterior end of the fourth ventricle, in the aquceductus Silvii, and in the lateral ventricles. The remaining parts of these regions are lined by simple pavement epithelium of more or less rounded cells, in the adult individual. The plexus choroidei and telai choroidaie are covered by that modified rounded pavement epithelium men- tioned already in an earlier section (§ 88), though in the embryo they are clothed with ciliated cells. In conclusion, Ave find a stratum of flattened epithelium cells, arranged simply or in layers, and coA^ered with cilia, in the Eustachian tube and cavity of the tympanum, which gives.way on the surface of the latter, however, to a multilaminar pavement epithelium. Pigmentary ciliated cells are unknoAvn. Ciliated epithelium appears to possess a limited physiological poAver of renovation. " Goblet-cells " are frequently met with among them (Schulze). §94 Any chemical examination of epithelium to meet adequately the require- ments of present day histology Avould have to undertake the analysis of cells and intercellular substance, as Avell as that of the nucleus, body, and envelope of the latter, should it be present. It Avould have to shoAV also what the changes in chemical constitution are Avhich the youn«- cell passes through in laminated epithelium, Avhile undergoing transformation into the scale-like formations of the older and more superficial layers. But these theoretical requirements cannot be responded to, in that we possess no means of isolating the several portions of epithelial tissue from one another, and can only subject the whole mass in the form of a mix- ture to analysis. In spite of all this, however, so much is certain, that epithelium is a tissue which, in its simpler forms and younger layers is made up of cell-bodies, consisting frequently of protoplasm, Avhile'in epithelia of greater thickness the superficial layers undergo chemical transformation to a considerable degree, owing to which they become hard dried, and more consistent, i.e., become converted into corneous matter or keratin (§ 14), or, as the saying is, become horny Many non-laminated pavement epithelia, together with cylinder and ciliated cells, display the ordinary characters of elements formed of unstable protoplasm, the action of water even causing changes in the cell, such as puffing expulsion of spherical drops, and bursting of the envelope On the o her hand, numbers of simple pavement epithelia resist the action of both cold and hot water, and are affected only by acids and alkalies earlier or later, after which the protoplasm is changed, thou£ a JSj of it may remain unaltered around the nucleus. The latter usually offers a determined resistance to the action of acetic acid The bearing of the deeper or younger cells of laminated epithelia agrees TISSUES OF THE BODY. 153 Avith the description just given, while the more superficial scale-like forma- tions, at one time nucleated, at another not so, give the reactions of keratin. This represents, naturally, a mixture of substances; it forms the nucleus, contents, envelope of these elements, and the scanty intercellular matter; the residue after treatment with Avater, alcohol, and ether. This mixture is then insoluble in cold as Avell as boiling Avater, and (if not contaminated Avith other elements of connective tissue) yields no glutin on boiling; nor is it acted on by acetic acid. Even to sulphuric acid, in Avhich it becomes puffy, it offers a certain amount of resistance. With hydrochloric and sulphuric acid it gives the reactions of the protein sub- stances. Its conduct toward alkalies is, however, of the greatest importance: with them keratin enters into combination, at the same time that it puffs out or becomes gelatinous, and is subsequently dissolved on the addition of water. If to such a solution of keratin acetic acid be added, certain products of the decomposition of the albuminoid group are precipitated. The swelling up of this tissue before solution, as it occurs both in cold and heat, has much interest for the anatomist (fig. 150). In order to produce this appearance, we treat the epidermis either with a very strong caustic solution, and then with Avater, or Ave employ from the commence- ment more dilute reagents. On this the older cells become puffed out into spheroids (1 b-f, 2 b, c), lose their flattened figure, and again assume, in the most striking manner, their original cellular character, the contents beginning to dissolve in the imbibed fluid, and the envelope to become sharply defined. At the same time, also, the stratification of the epithelial beds becomes distinctly visible, so that in this respect likeAvise alkalies may be of the greatest service to microscopists. Later on the nucleus is attacked (1 b-d), and then the intercellular matter. Finally the envelope is dissolved, but only if the ced be not one of those which have been completely converted into horny matter. Very old squam- ous elements possess, on the other hand, a mem- brane Avhich reminds us in its great capacity for resistance to alkalies, of the substance of the elas- tic tissues. The addi- tion of acetic acid pro- duces in the cell Avhich has gelatinised in the manner described, a precipitate of decom- posed protein substances already mentioned (1 g, 2d). After Avhat has just been remarked, there can be hardly any doubt that keratin partakes of Fig. 150.—1. Epithelial cells. At a, an unchanged fiat cell from the mouth; from 6 to/, the same kinds of cells after treat- ment with caustic soda, some containing nuclei (6 c d) and some not; g, on the addition of acetic acid, after treatment with caustic soda. 2. Epidermal cells, a, unchanged; b. commencing action of the soda; at c, after prolonged action of the same; d, on the addition of acetic acid. 154 MANUAL OF HISTOLOGY. the nature of a mixture, so that its present analyses are almost worthless. We may take, for instance, those quantitative ones of Mulder and Scherer, which apply to the epidermis of the sole of the human foot. (Scherer.) (Mulder.) C 51-036 50-752 C 50-28 H 6-801 6-761 H 6-76 N 17-225 17-225 N 17-21 0 " 0 25-01 s ■ 24-938 25-262 s 0-74 The amount of sulphur (0-74 per cent.) in Mulder's analysis appears strikingly small, while it is found to rise to between 2 and 5 per cent, in the keratin of other tissues. As to the form in which it is contained in the latter we know nothing. It is, however, only loosely combined. The proportion of ash rises to about from 1 to 1 -5 per cent. The salts obtain- able are chlorides of sodium and potassium, sulphate and phosphate of calcium, phosphates of magnesium and of iron, besides which silicates are also contained in the epidermis. The pigmentary cells possess the same characters as all the other eprthelial formations. Those of the eye correspond in their delicate con- stitution with the non-laminated epithelia. In regard to the melanin with which they are charged, comp. § 37. Finally, we are still quite ignorant as to what the matter is with which the nuclei of epidermal cells, of dark spots of the skin, are coloured. §95. The elements of epithelium stand in very close genetic relationship to the gland-cells. Remak has shown that both tissues have their origin from those two layers of cells continuous with one another,^which clothe the internal and external surfaces of the embryonic body. There like- wise exists frequently between the epidermal elements and gland-cells of the mature body a gradual transition: many glands, namely, are lined with cells which can hardly be distinguished from those of the epithelia. On the other hand, as a feature in epithelial life, the formation of mucus has much in common with the destiny of certain gland ele- ments ; and those goblet-cells mentioned above (§ 92) may be named single-celled glands. Finally, the tendency which they both display to excrete amorphous matter, as for instance, the thickened cell-border or that which hardens into the membrana propria or basement membrane, may perhaps be regarded as another feature common to the gland and epidermal cells. The genesis of these two structures, however, must be more fully ascertained before Ave can unreservedly adduce it as additional proot ol this relationship between the two. Now! Wfien^e ques^ arises as to the purposes which epithelium serves m the body, and why all the surfaces of the latter are clothed with such a continuous cellular coating, we must confess ourselves in a difficulty in ascribing to each species its particular properties ' If we look for a physiological significance in our tissue, it may be said to have its basis m all probability in the relation of the latter to the nrocesses of transudation, diffusion, and absorption of the economy and TISSUES OF THE BODY. 155 we may perhaps regard epithelium as the regulator of these processes spread over the parts where they take place. As a purely cellular tissue untraversed by blood-vessels, epithelium presents to us many sides of cell-life in the most beautiful manner, such as multiplication, groAvth, and change of form. That the whole vegetation of the epithelial cells is dependent upon the vessels of their connective- tissue substrata is easy to conceive, though we meet with epithelia on non-vascular portions of the body, as for instance on the cornea and capsule of the lens. But of the direction of the interchange of matter in our tissue we know nothing, either of that in ordinary epithelium, or the modified forms of it, where in the interior of the cells a formation of melanin and other pigments takes place. That this alteration of material in laminated epithelium is only undertaken Avith any degree ol energy by the younger cells Avhich still possess soft contents, is more- over not difficult to understand. It is also probable, on the other hand, that this interchange of material has ceased entirely in the more superfi- cial scales of laminated epithelia which have undergone horny metamor- phosis : in these also decomposition commences very late. Then the cylinder epithelial cells of the small intestine are made the media for much transfer of matter, and moreover, not in their own egotistical interest, and for their OAvn special support: through them, namely, the absorption of fats with the other constituents of the chyle takes place. Here again we are reminded of many kinds of gland- cells. Attention has likewise been directed within the last few years to the penetration into the interior of epithelial cells of minute coloured par- ticles, Avhich had been introduced into the circulation of the lymph and blood, and, indeed, of red blood-corpuscles also (1). These we may observe in the goblet-cells of the small intestine and in ciliated cells. We are obliged for the present to explain the fact of the occurrence of mucous and pus corpuscles, as Avell as of contractile elements, in the interior of cylinder and pavement epithelium (fig. 151) in the same manner (§ 56). It is manifest that a penetration of small bodies into open goblet-cells might take place without difficulty. But, besides, we find these lymphoid-cells within the epithelial stratum, betAveen the columnar ele- ments of the intestine, engaged in mi- grating from the connective-tissue of the mucous membrane into the lumen of the tube. Epithelium may, in general, be set down as a tissue capable of under- going no further development. No doubt from the earliest rudiments, from the cells of the corneous and intestinal glandular layer, many other tissues, and some of them of high dignity, take their origin in the construction of the embryonic body, as we shall see in some of the succeeding chapters. But not so in the mature body: its epithelial cells are only able to reproduce similar structures, and not other elements, such as, for instance, fat-cells or connective-tissue corpuscles. Fig. 151.—Occurrence of mucous and pus- corpuscles in the interior of epithelial cells, a-d, cylinder ceils of a biliary duct; «, free pus-coipuscles; /, ciliary cells of the respiratory tract; g, flat ceils from the urinary passages. * 156 MANUAL OF HISTOLOGY. The destruction of epithelial cells is brought about, first, by solution, nextly, by mechanical attrition. This naturally deprives the system dady of a certain quantity of albuminoid matters, though in an altered condition. Remarks.__The question as to a connection between epithelial cells and the ele- ments of connective substances and of nerve-tissue, must be discussed in a future section.—1. 1 have com-inced myself of the presence of granules of cinnabar in the cylinder cells of a frog's intestine, three days after their injection into the circula- tion. §96. OAving to their composition decaying epithelia are of the greatest im- portance in the formation of mucus. The consideration of these tissues must, therefore, extend itself over fluids likewise. We understand by mucus a coating of a rather thick semifluid sub- stance, more or less stringy and tenacious, Avhich covers the surfaces of all mucous membranes in varying quantity, and endows the latter with their usual moistness and smoothness. It must also be regarded, owing to its consistence, as well fitted to form a protecting medium against chemical action, and it is probably not indifferent, besides, to the inter- change of gases. Mucus is without odour and tasteless, and variable in its reactions. It is found sometimes transparent, sometimes more opaque, Avhite or yellowish. Microscopical examination discloses to us in it the cast off epithelial and gland-cells of the locality in which it is formed, but in variable number; and besides these a small cell, the so-called mucus-corpuscle, Avhose appear- ance, size, and bearing repeats the colourless blood-cell completely, as well as the elements of chyle and lymph, and Avhose origin, as far as is at pre- sent knoAvn, may be \~ery various. It may spring not only from epithelial cells, but also from those of connective tissue and lymphatic organs. To these are added the cells of the glandular formation of the part from Avhich the liquid is obtained. Again, owing to its viscidity, mucus entangles usually a number of very minute air-bubbles. From all this it Avould appear that mucus is a most variable substance. From an ana- tomical point of view it is only a mixture of many dissimilar matters, and amongst others of various gland juices, which endoAv it further Avith chemical differences, as an expression of Avhich we recognise the multi- farious fermenting properties of the several kinds of mucus. Chemical anaylsis discloses as a solid constituent a peculiar substance already mentioned (§ 14) known as mucin. Besides this Ave find extrac- tive matters, fats, and mineral constituents. Among the latter chlorine, phosphoric, sulphuric, and carbonic acid, silicates, lime, and soda are said to exist in mucus. The folloAvin^ table from Nasse may be taken as an example of its quantitative compose tion. By subjecting human mucus, Avhich had been coughed up, to analysis, he obtained the following results :— Water,.......955-52 Solid constituents, ..... 44*48 Mucin (and a trace of albumen), . . 23-75 Extractive matters, . . . , t 9.32 Fats>.......2-89 Mineral constituents, . . . , g-02 * TISSUES OF THE BODY. 157 Of all these components mucin alone requires further consideration. It appears in mucus under two forms: as an insoluble substance, merely gelatinising in Avater, and Avhich remains behind on a filter; and as a soluble matter Avhich may be filtered. jSoav, in that the reactions of both are the same, we are Avarranted in supposing that mucin in a pure state is insoluble, and has probably acquired its solubility by admixture Avith other compounds, especially alkalies,—an hypothesis Avhich appears to receive further support from its parallelism Avith many protein matters in this respect. Synovia also reminds us of mucus (Frerichs). We meet it as a clear, colourless, or straAV-coloured fluid of slimy consistence and alkaline re- action, in Avhich the microscope reveals to us the epithelial cells of the capsule of the joint, Avhich have been shed, as avcII as lymphoid cor- puscles. The use of this liquid is, as is Avell knoAvn, to retain the parts entering into the formation of the joint in a moist and slippery condition. Synovia, strangely enough, has farther the same constituents as mucus, in addition to Avhich. albumen is also present. Of salts we find, chloride of sodium, basic phosphates of the alkalies, sulphates of the alkalies, phos- phatic earths, and carbonate of calcium. The two folloAving analyses of Frerichs may serve as an example of its composition per cent. The first applies to the synovia of an. ox fed in the stall, Avhile the second is that of one in pasture:— I. II. Water, . . . . . 969-90 948-54 Solid constituents, . . . 30-10 51-46 Mucus Avith epithelium, . . 2-40 5-60 Albumen and extractives, . . 15-76 35 12 Fats.......0-62 076 Salts, .... 11-32 9-98 According to this, it Avould appear as though the friction of the surfaces of the joints induced by exercise Avere of importance in the formation of synovia, for Ave find it during inactivity, Avatery, less viscid, and poorer in mucin. At the same time, however, its quantity is far more consider- able. Again, on energetic bodily exertion the quantity of this fluid decreases considerably, and the amount of mucin increases, with its oiliness or thickness. The contents of bursas and the sheaths of ten- dons appear, also, according to Virchow, to be allied to synovia in com- position. Noav, as to the formation of mucus and the origin of mucin parti- cularly, the older vieAvs, Avhich referred both exclusively to the secretion of special glandular organs, the so-called mucous glands, can no longer obtain, in that the proportion of the fluid stands in no relation to the frequency or rarity of those glands; and in that synovial capsules, Avhich have none of the latter, nevertheless secrete mucus. Epithelial cells, however, appear to stand in close relation to the origin of mucin, beside Avhich the elements of the glands themselves, Avithout doubt, play a part in the formation of mucus. There seems, indeed, much probability in the supposition, that an alkaline fluid transuding through the capillaries of mucous membranes macerates the cast-off cells, aided by the natural 158 MANUAL OF HISTOLOGY. warmth of the body, and thus transforms their contents into mucin (Simon, Frerichs). If this mode of explaining its origin be correct, mucin must represent in numerous cases a physiological transformation product of epithelial tissue. §97. To what extent epithelial cells are endowed with the property of vital contractility, Avhen young and still soft, we are for the present unable to state. But a most remarkable movement is met with on the other hand in ciliated epithelia, which has been named ciliary motion (Moius vibra- to ius). This phenomenon, knoAvn from the earliest epochs of microscopic research, has been recently very closely studied, but unfortunately with but small results. For although its wide distribution throughout the animal kingdom has been recognised, and ciliary motion not long since observed in low vegetable organisms, Ave are still completely in the dark as to its mechanism and object. The elucidation of points of this kind regarding it are rendered thus difficult by the fact, that the phenomenon of ciliary motion is met Avith in very varied extent throughout the animal kingdom, parts which are ciliated in one class being no longer so in another group ; thus, for instance, none of these cells can be found among any of the arthropoda. Ciliary motion, a simultaneous and regular swinging of all the minute hairs, appears, as seen on the edge of a fold of membrane, somewhat like to the undulation of a shaken cloth, or the flickering of a candle flame. Seen from above it frequently reminds us of the waving of a field of corn moved by the Avind, or when it takes place in a tube of extreme fineness, of the current of a brook in the sun light. All these comparisons, however, are perhaps hardly adequate to express the pecu- liarity of the appearance. Small particles suspended in Avater—as, for instance, blood-corpuscles and pigmentary granules—are driven along by the movements of the cilia at the edge of a membrane possessing them in one definite direction, and apparently with great rapidity when the action is energetic, and the magnifying power great. In reality, however, this rapidity is much less than it seems, but still by no means inconsiderable, for an interval of an inch may be traversed by one of these particles in a feAV minutes. Even a shred of a ciliated stratum of cells may be driven along by the motion of its own particular cilia, if it be not altogether too large, Avhile a smaller piece, or single detached cell, may whirl itself through the water in a lively manner, simulating in a most deceptive way the motions of the infusoria. However, in a fresh state, and when the cilia are endued with great vital energy, the motious of the hairs folloAv so rapidly in succession, that the latter are not seen, nor can the phenomenon be recognised as a rule. Several vibrations are usually observed to take place in "the course of a single second. For the closer examination of the phenomenon that moment is most suitable at Avhich the movement of the cilia has become slower and weaker, owing to the approaching death of the cells, and when each individual little hair may be observed for itself. | The mode in which it is carried out is not always the same, so that the motion has been classified into four varieties (Purkinje and Valentin), namely, into (1) the hook- like (hakenformige), in which each cilium makes the movement of a TISSUES OF THE BODY. 159 finger Avhich is alternately bent and extended; (2), the funnel-shaped (trichterformige), in Avhich the upper portion of the hair describes a circle in swinging, and the whole a cone, whose apex is formed by the firmly attached base of the cilium ; (3), the oscillating, in which the whole hair sways more like a pendulum from side to side; and (4), the und,ulating. In this the hair executes a movement like the lash of a Avhip moderately wielded, or the tail of a spermatozoon. Of all these forms of ciliary motion the first appears to be by far the most frequent (2). \ This movement appears quite independent of the circulatory and nervous systems. Destruction of the latter or interruption of the stream of blood causes no cessation of its activity. The cilia, also, of detached cells persist in their oscillation still, as Ave have already remarked. Should they, hoAvever, become separated from their cells they cease to manifest vitality, and soon disappear completely in the water surrounding them. Ciliary motion, farther, is of longer duration than the life of the animal, but with extraordinary differences. Sometimes it only lasts a short time, especially among birds, and also mammals, Avhere it continues about until the cooling of the corpse, whilst among cold-blooded animals it may be observed for days (3). Elevation of temperature increases the energy of this movement, until finally at from 44° to 45° C. coagulation commences. On the other hand, cold has a retarding and finally destructive influence, while agents which do not act chemically do not disturb it in the least. Thus it continues unimpeded in serum, milk, and also in urine. Water accelerates ciliary motion at first, but subsequently puts an end to it rapidly, owing to its action on the very delicate cell. The addition of bile produces an injurious effect on it also, Avhile that of alkalies, acids, alcohol, and such like, put an end to it for ever. A very interesting discovery was made not long since by Virchow, that ciliary motion Avhich has come to a state of rest under normal conditions may be again excited by the application of dilute solutions of soda and potash (4). The influence of gases on the phenomenon has also been lately investigated by Kiihne. It appears that like protoplasmic contractility, to which they are akin, the motions of the cilia require oxygen for their support, and that hydrogen causes them to cease. They may be again set agoing by the introduction of a stream of oxygen into the medium in which the cells are immersed. Acidulation also with carbonic acid has a retarding influence on the ciliary motion, counteracted again by alkaline vapours. The retarding effects of alkaline vapours can also be met by acid ones. There seems to be an inclination to bring this ciliary motion physiolo- gically to bear upon the transport of small bodies, and to ascribe to it, for instance, the poAver of forwarding mucus from the nose and lungs, and the ovum from the ovary into the uterus. But these are surely only incidental objects of ciliary motion, which receive their just value when we take into consideration the fact that coatings of ciliary cells occur in completely closed cavities. That the little hair-like appendages may effect a change of locality of the Avhole body, however, of lower organisms, or induce a motion in the Avater in contact with the surface of the latter, or, finall}', a rotation of alimentary matters in their digestive tract, &c, is beyond doubt. Remarks.—1. The discovery of ciliary motion appears to have been made by A. de Heyde, in the year 1683*; and the Dutch Coryphsei of former days were also acquainted with it. But the most accurate studies, dating from 1830, in which this 1G0 MANUAL OF HISTOLOGY. subject Avas first treated with effect, Avere made by Purkinje and Valentin, comp. De phccnomeno generali et fundamentali motus vibratorii continui in membranis cum externis, turn internis animalium plurimorum et superiorum et ivferiorum ordinum obvii comment, phys. Vratislavice, 1835.—2. According to Englemann's varying observations, this swinging of the cilia depends upon two motions of unequal length,— upon a longer one produced by the contractility of the protoplasm, and a shorter one caused by elastic resistance. Currents of fluid"passing over ciliated surfaces do so in the direction of the last of these, in which also the cilia stiffen after death.—3. Under certain circumstances, difficult to explain, the ciliary motion may persist for one or two days after the death of a mammalian animal.—4. As Koelliker has demonstrated, the same peculiarity is displayed by the spermatozoa. §98. Now, as to the origin of epithelium in the embryo, we must enter here at somewhat greater length upon the consideration of the relations of parts briefly touched on already at § 86, in order to obtain a clear con- ception of its development. As we have already seen, the rudimentary embryonic body according to Remak (1.) consists of three layers of cells, of the so-called leaves or germinal plates. These are known as the superior or the corneous, the in- termediate or middle germinal, and the inferior or intestinal glandular leaf or plate. From these the Ararious tissues and organs of the body take their rise. The corneous plate produces, first of all, the epithelium, Avith the nails and hair Avhich are closely allied to it, and beside these the crystalline lens, a decidedly epithelial organ. The cellular elements, likeAvise, of the various glands of the skin, together Avith those of the mammary and lachrymal organs, take their origin from the same layer. Finally, the axial portion of the corneous plate enters into'the construction of the nervous centres (brain and spinal cord) as Avell as the internal portions of the higher organs of sense. That the peripheral nerves also originate in the axial part of the corneous plate primarily, is at least probable. (2.) The significance, consequently, of the corneous plate is very great, physio- logically the highest in the body. Thus a large part of the epithelium described in former sections, the epidermis, including those layers of cells which clothe the openings of the larger passages of the body, takes origin from this source, and appears as laminated epithelium, with a horny substance devoid of vitality. The pigmentary pavement epithelium also, of the eye, together with the internal coating of the cavities of the nervous system, are also derived from this superior plate. The second, or intestinal-glandular plate, supplies the epithelia of the digestive apparatus, as well as the cellular constituents of all the "lands in connection with the latter, including the lungs, liver, and pancreas. Its epithelial formations appear principally in the form of the cylinder- cell, either naked or ciliated. We must now finally devote a few moments to the middle germinal plate, and inquire after its contributions to the epithelia This middle stratum of the rudimentary embryos supplies material for a great many structures. First of all, for the formation of all the tissues of support in the system, the Avhole group of connective substances; for the building up of muscle; for the blood and lymph, together with the so complicated system of vessels which contains both; and finally, for the so-called lymph or blood-generating glands (including the spleen) The cutis TISSUES OF THE BODY. 161 vera containing the vessels of the dermis, with the connective tissues of mucous membrane and true glands, take their rise from this source. It is evident that the changes must be very great in the middle layer Avhich produce from it such structures. To many of these changes Ave shall have to refer again in subsequent pages, but for the present our attention must be principally directed to the formation of numerous cavities in the middle plate appearing in the course of its development. Thus it is that the serous sacs originate, as also the bursas and sheaths of tendons. Thus is formed the most intricate of all systems of canals, namely, that of the blood and lymphatics. Together Avith this formation of cavities, also, Ave must expect besides to find a Avhole scries of epithelial coatings springing up. The latter have much about them that is peculiar. If Ave except the more circumscribed laminations as they appear in synovial membranes, they almost always consist of a single layer of thin flat scales (§ 87) Avith- out the transient nature of the tAvo other forms of epithelium. Further, as observation of the circulatory system teaches, such an epithelial tunic may acquire sufficient strength by cohesion of its cells, as to fit it to form the chief part of the finer and more minute canals of the former. But these epithelia of the intermediate germinal plate do not possess the power of yielding in continuous transition the secreting cells of glands, nor are they able to develope any physiological function similar to glandular activity. On the other hand, they are remarkable for the great ease with which the fluids of the blood transude through them, which is far from the superficial layers of cells of the epi- dermis; b, the deeper; m m, cells of the Fitr. 153—Epidermis from the neighbourhood of rudimentary hair; i, transparent mem- the head of a sheep-embryo of 4 in. in length. brane clothing them. 1, epidermal cells of the most superficial layer; 2, from deeper lamina; 3, vertical section of the same; 4, cuticle from the free edge of the eyelid. being the case Avith the epithelial structures of the corneous layer. If we are asked for another contrast, it is to be found in the nonvascularity of the subjacent tissue of this last species of epithelium compared to the great vascularity of the other tAvo kinds. This intermediate species has been termed false epithelium, or endo- thelium, by His. As regards tho epithelium of the corneous layer, Koelliker found the epidermis in the human embryo of five Aveeks old to consist already of two laminae of nucleated cells : a superficial, made up of delicately- edged polyhedral elements of 0-0275-0-0451 mm., Avith round nuclei, measuring 0-0090-0*0136 mm. ; and a deeper layer, in which the cells 162 MANUAL OF HISTOLOGY. Avere smaller, about 0-0068-0-0090 mm. in diameter, Avith nuclei of only 0-0034-0-0045 mm. From this we see that the epidermis, properly so called, and the rete Malpighii, are each formed originally of one layer of cells. Later on in the fourth month these are slightly laminated, the whole epidermis consisting of three or four strata (fig. 152, a b). From this on the lamination becomes stronger by degrees. Let us take, for example, the epidermis of a foetal sheep 4 inches long (fig. 153). This consists of six or seven layers of cells (fig. 153), of which the most superior (a) are transparent, and measure 0-0156-0-0206 mm., with nuclei 0-0052-0-0066 mm., Avhilst the deeper (b) are only 0-0104-0-0124, the nuclei preserving the same dimensions as in the more superficial lamhice. In the superficial strata are found scattered cells with a double nucleus (fig. 153, 1), and division of the latter may be remarked at times in those lying deeper (2). The epithelium on the free edge of the eye- lid shows in this embryo but two layers of cells (4). I have found the epithelium of the cornea also in a human foetus four months old 0-0205 mm. thick, and consisting of two upper and two lower layers of cells. With the further growth of the foetal body, the thickness of the epi- dermis and the number of its laminae increase more and more, and the most superficial of the latter already resemble the scaly non-nucleated structures of later year3, before the close of the second half of intra- uterine life. CDcsquamation of the cuticle commencing in embryonic life, produces upon the body of the child a coating of a greasy Avhitish substance, intermingled Avith fat, known as the vernix caseosa, in which the micro- scope reveals to us the scale-like epidermal cells. , The epithelia, also, of the intestinal glandular plate likewise evince at an early period a disposition to assume their characteristic forms. The increase of the superficial extent of these coverings necessitates likewise multiplication of the cells by division. That the endothelia also make an early appearance has been already observed above, where Ave have also considered the cells from Avhich they take their rise. Remarks.—1. Comp. the Avork on embryology of this investigator.—2. In a re- cent work His points out that from a superior germinal plate the nervous system, animal muscles, Wolffian bodies (the kidneys and sexual glands), take their rise together with the epidermal structures and cells of external glands. A subse- quently formed inferior plate gives origin to the sympathetic system, unstriped muscles, epithelia, and glands of the mucous membranes. These two plates con- stitute his " archiblast." Between them the "parablast" is then inserted, from which connective tissue and blood are formed. For the present we prefer adhering to Remak's views. 4. Nail. §99. Like the epidermis and the hair, to be considered farther on, the nails have long been placed by anatomists among the horny tissues. And, indeed, they represent nothing more than a peculiarly modified cuticle for the part of the skin lying underneath. But the transformation proves to be less on microscopic investigation than we might have expected from the physical constitution of the tissue. The nail is a hard, flat and arched body of rounded quadrangular TISSUES OF THE BODY. 163 shape. It is more strongly doubled down at the sides than in the middle; and at the anterior free edge is thicker than posteriorly. Fig. 154.—Nsil and matrix in transverse section, a, the matrix with the ridges of the cutis; 6, side portion of the same, forming the groove of the nail; c, rete Malpighii; e. hoiny layer; d, rete Malpighii of the nail, dipping in between the papilla of the matrix; /, the horny substance of the nail. Of the edges only the anterior is exposed, while the lateral ones are concealed in a fold of the skin (fig. 154, b) which commences at the point of the finger as a flat groove, and becomes deeper and deeper behind. The posterior portion of the nail finally disappears in a very " deep furrow of about 4-5 mm. in depth (fig. 154, a left), in which a con- siderable proportion of the whole nail is contained, knoAvn as the " root" (fig. 155, I), while the lateral grooves have received the name of "the fold,"and the portion of skin concealed by the nail, that of " the matrix" (fig. 154, a; 155, a). Fig. 155.—Nail and matrix divided vertically and longitudinally, a, the matrix, forming at the left hand side the deep fold for the root, I; k, the horny part of nail; m, its anterior free edge; / epi- dermal layer on the point of the finger; g, its termination towards the rail; b, rete Malpighii of the same, which becomes that of the nail at c, and of the fold of the nail and root at d; while at e, it is continuous with that of the dorsum of the finger; h, epidermal layer on the dorsum of the latter; i, termination ofthe same towards the nail. The nail, which determines, roughly taken, the form of the matrix in conjunction Avith the lateral fold, is so closely adherent to the first of these that, like the rete Malpighii on other parts of the fibrous tissue of the cutis, it can only be separated from it by maceration or boiling. If Ave examine the surface of a matrix so exposed, we find it marked by a number of longitudinal ridg'es. These, as Henle has demon- strated, commence at the posterior border of the matrix as from one pole, and, in the middle portions, pass directly fonvards to the anterior edge, while at the sides they maintain a course convex exter- nally. On these ridges are situated, more or less isolated, the papillae of the cutis. Fig. 154, d, represents the former, of which from 50 to 90 may be reckoned on one matrix. They are arranged much closer to- gether under the root of the nail than elsewhere, but are, at the same time, much less elevated there. Both parts of the matrix are usually 164 MANUAL OF HISTOLOGY. sharply defined one against the other by a curved line, which is visible through the nail as the edge of the so-called lunula. Now, as Ave have already remarked, the rete Malpighii dips doAvn Avith jagged projections into the intervals betAveen the ridges of the cutis; it conducts itself consequently just as at any other part of the skin (fig. 154, d). Tho young cells of Avhich it is composed correspond also in their histological constitution Avith those of the external skin (fig. 156,/). In size they range betAveen 0-0090 and 0-0160 mm., and their nuclei between 0-0065 and 0*0075 mm. The only difference appears to be, that in the deepest layers the cells of the younger lamina* are apparently more or less oval. According to C. Krause, the nuclei of such nail cells contain, in negroes, the same dark brown pigment as the skin itself (§ 90); a fact of much interest. Cells Avith a double nucleus are not unfre- quently met with here also (g). That the rete Malpighii of the nail is conti- nuous with the younger cells of the epidermis in the furrow, and at the point of the finger, hardly requires to be mentioned, and may be seen in fig. 154, c, and 155, b. Noav, while the cells of the deeper layers have but little about them that is striking, the reverse is the case Avith those of the superficial laminae or true horny substance of the nail. Generally speaking, Ave have only to remember that the under surface of the horny layer clings, by means of slight indentations, to the rete Malpighii (fig. 154, /), and that on the root of the nail it is con- siderably thinner and softer than the free uncovered portion. Finally, the epidermis of the skin passes fonvards a certain distance on the surface of the nail from the inferior fold (fig. 155, i), Avhile that of the tip of the finger is lost under the free edge of the same (fig. 155,/). Sections of this horny substance give no clue to its texture with- out further treatment; for Ave have to deal Avith a brittle, hard, and tolerably transparent mass, which appears, to a certain extent, split up and torn by the edge of the knife. If Ave subject such a section, how- ever, to the action of sulphuric acid, or, still better, to that of caustic soda or potash, the Avhole of it swells up in a very remarkable manner (especially when Avarmed) into the most beautiful epithelial tissue (fig. 156, a-e). At first tho cells are marked off one against the other, as flat- tened polyhedra (d); but eventually they separate from one another, under the continued action of the reagent. Their size is usually 00375-0-0425 mm. But though they correspond so far Avith epidermis cells, the elements of nail-tissue possess one distinguishing characteristic (if the chemical action of the reagents have not gone too far), in the form of a rounded granular nucleus, a delicate lenticular structure, seen in fig. 156, b, c, d, e, from above, as compared Avith the side view at a. Its diameter lies between 0-0075 and 00090 mm. Fig. 156.—Tissues of the human nail, mostly after treatment with caustic soda, a, cells of the superficial layer in profile; 6, one seen from above; c, half profile; d, a number of cells, of polyhedral outline, in contact with one another; e, a cell whose nucleus is about to disappear; /, cells from the undermost part of the rete Malpighii; g, one of the same kind, with double nucleus. TISSUES OF THE BODY. 165 §100. The nails of the human being differ from the epidermis in their greater hardness and solidity, but correspond very essentially with the latter in their chemical relations. Like the scales of the cuticle, they yield on treatment Avith alkalies keratin, already mentioned (§ 94). Analyses of the substance of human nail-tissue have been frequently made ; of those available Ave will only quote the folloAving, from Scherer and Mulder:— Scherer. Mulder. C, . . 51-09 51-00 H, . . 6-82 6-94 N, . . 16-90 17-51 S, \ • 25.19 ( 2-80 O, / . w0 iy { 21-75 According to these, the proportion of sulphur in the keratin of nail- tissue appears more considerable than that of the epidermis, in which it only amounts to 0-74 per cent. (p. 152). The proportion of mineral con- stituents was found to be 1 per cent. The tissue of nail, like that of the cuticle, is nourished by the blood- vessels of the matrix and furroAv, and shows, in our condition of culture, a constant and tolerably lively growth, exceeding by far the loss of sub- stance induced by the ceaseless Avear and tear going on at the free edge. It appears, however, that Avith those who do not pare their nails, as, for instance, the Chinese, the groAvth of the former reaches a limit eventually, for those talon-shaped nails, of about two inches in length, sometimes met Avith, do not increase any more, according to Hamilton. According to E. H. Weber, the free edge is cast off at times in children in the form of a crescentic strip. Some interesting experiments Avere made by Berthold in regard to the amount of growth of the nail, or, Avhat is the same thing, into the length of existence of a horny cell of the latter. Regeneration takes place, according to this observer, more rapidly in infancy than at an adAranced age, and in summer than in winter; a nail, Avhich requires during the Avarm part of the year 116 days for its complete renovation, consuming 152 days in the latter process during the Avinter. The nails also of different fingers, as avcII as those of corresponding members on the right and left hands, are said to be dissimilar in growth also. The mode in Avhich they groAv is as follows:—The deeper cells of the rete Malpighii preserve their position, Avhilst the horny lamina is pushed for- Avard over the softer layer of cells covered by it, by the constant production of new elements at the posterior border of the root, Avhich become trans- formed into scales. That the nail anteriorly is considerably thicker than behind is explained by the fact that the more superficial cells of the rete mucosum are also transformed on the surface of the matrix into horny lamina", which unite Avith the under surface of the completed corneous portion of the nail, strengthening' the latter, and naturally pressed for- Avard Avith it. Noav, just as there is a normal physiological renovation of the nail, so do Ave find that the latter may be completely regenerated after having been lost in an abnormal manner, provided that the matrix have preserved its integrity. If the latter have suffered, an ill-formed nail is produced. And further, in that tho nail is dependent for its groAvth on the vessels of the matrix, it is easy to conceive hoAv many affections combined with 166 MANUAL OF HISTOLOGY. disturbances in the circulation of the latter may lead to its malforma- tion. The nails, likeAvise, are shed from the extremities among rabbits, as Steinriick's well-known experiments have shown, after division of the sciatic nerve. The fact also observed by Koelliker is very interesting, namely, that in those cases in Avhich we find thickening and malforma- tion of the nails of elderly individuals, the capillaries of the anterior por- tion of the matrix may be impervious, owing to a deposit in them of fatty granules Finally, as to the first appearance of the nail in the embryo, Ave find its rudiments in the third month of inter-uterine existence in the form of a fold in the usual situation, which is clothed with the ordinary cells of the embryonic skin. Then in the fourth month, under the embryonic epider- mis, and above the rete Malpighii of the matrix, a layer of neAv cells is seen, destined to become the horny cells of the future nail. Later on, more of the same kind of strata are deposited on these, so that the corneous layer, although still soft, acquires considerable thickness. At the end of the fifth month the coating of simple epidermal scales has dis- appeared from over the nail, and the latter lies freely exposed. In the nail of the new-born child we may still recognise its cellular nature Avith- out the aid of reagents, but after the first year the cells are of the same constitution a"s in the adult body. C. Tissues belonging to the Connective- Substance Group. §101. Having discussed the epithelia, we now turn to the consideration of another natural group of textures, namely, the connective-substance group, one of the most important, but at the same time most difficult chapters of histology. This name has been given by the greater number of investigators of our day to a series of tissues, all of which probably take their origin from the so-called middle embryonic plate, and start from the same rudiments. They usually, however, in the course of their farther development in various directions, become separated further and further from one another, taking on the most diverse forms, as well from a chemical as anatomical point of view. Thus, in the mature organism, there occur in the connec- tive-substance group masses which appear at the first glance to be sepa- rated by a very wide gap. Among these may be reckoned cartilage, mucoid or gelatinous tissues, recticular connective-substances, ordinary con- nective tissue, fatty tissue, bone, and the substance composing teeth or dentine. The near relationship, however, of all these different tissues is not to be denied. In the first place, we often see,—though the typically marked varieties of these several tissues may differ widely from one another,—intermediate forms, as, for instance, between gelatinous and ordinary connective tissue and between the latter and cartilage; so that a sharp line of demarcation cannot possibly be draAvn betAveen the various members of the series Again, in many regions of the body, these several tissues merge one into another, as, for instance, in the case of those just mentioned. Further, a substitution or replacement of one tissue by another equi- valent one has been remarked, and moreover of threefold nature. TISSUES OF THE BODY. 167 ✓ In the first place, comparative histology teaches that the different forms which belong to this group of connective tissues replace each other frequently enough. What is in one animal, for instance, ordinary con- nectiA'e tissue appears in another in the form of reticular substance, cartilage, or bone. The cartilage of some organs in one being is replaced in the same parts of another by bone, or bony tissue by dentine, and so on. But in one and the same organism also typical development brings Avith it a substitution of one member of the connective-substance group for another. There, for instance, where in the embryonic state gelatinous tissue existed, the latter is found transformed into connective tissue or fat at a later epoch; cartilage with its derivatives takes on the form of bony substance. Finally, Ave encounter every kind of this substitution in the richest abundance in pathological reseaich, brought about by formative activity of a system modified by disease. Almost every member of the group of connective tissues may be replaced by very nearly any other, firstly by immediate metamorphosis, then again more particularly by reconstruction from the offspring of the original tissue. Noav, while we thus have sufficient examples of relationship on anatomi- cal territory, all the tissues of this group are also found to correspond in another respect, namely, from a physiological point of vieAv. Their signifi- cance in the actions of the healthy body is of a more subordinate kind, although they make up an enormous proportion of it. They represent, as is usually said, tissues of loAver vital dignity, certain connecting, enclosing, or supporting matters in our system, or a kind of widely distributed framework, in whose interspaces other tissues, as, for instance, muscles, nerves, vessels, and gland-cells, lie imbedded. The name, therefore, " con- nective-substance," formed after that of " connective-tissue " proposed by Muller, appears in many respects a suitable one. The term " sustenta- cular tissue" applied to it by Kolliker might also be recommended. HoAvever, though connective-substance takes but little part in the phy- siological occurrences of the mature and healthy body, as Ave have just said, it loses this character of quiescence and indifference in the numerous transformations and luxuriant groAvths of the diseased body, and becomes on the contrary the most active tissue of the Avhole system. We are indebted to Viixhow for having brought out, by an extensive series of observations, that it is principally from the tissues of the con- nective-substance group that most of the pathological new formations take their rise, " so that the connective-tissue Avith its equivalents may be regarded as the common germ-bed of the body." Rf.marks.—Science has to thank Reichert for having in the year 1845 placed our views as regards connective-tissue on a firm basis. §102. Xow, although it is comparatively easy to sketch the first outlines of the connective-substance group, definition in individual cases, and the arrangement of the A'arious forms of tissue by means of the history of their'development, is attended at present with the greatest difficulty. Indeed, the requirements of histology on these points can be only but very imperfectly satisfied in the present state of science. In the first place, there still exist great gaps, and then the earlier and more extensive 12 168 MANUAL OF HISTOLOGY. memoirs on the subject—as, for instance, those of Virchow, Bonders, and others—are no longer serviceable in the present condition of histology. And, finally, owing to the difficulty of investigation, and a certain amount of weariness produced by unprofitable discussions, the connective-tissues have recently been somewhat neglected by microscopists. The following are about all the features we can pronounce as histologi- cally characteristic of the group of connective substances :— The embryonic rudiments of all the tissues in question consist origi- nally of aggregations of more or less spheroidal formative cells, Avithout any membrane, and enclosing vesicular nuclei. Between these a soft, homo- geneous intercellular substance, consisting of albuminous matter, begins to be formed, be it as a product of the cells, or as a transformed portion of the cell-bodies. This appears later on in considerable though varying abundance. Subsequently the cells as well as the intercellular matter commence to take on other forms. As a rule, the ground-substance or matrix undergoes more or less a division into fibrous or stringy masses or a transformation into fibrillae, while the cells become stunted, or on the other hand develop into spindle-shaped or stellate elements, which again ' may unite to form a cellular net-work. Calcification likewise of the intercellular substance is a typical occurrence in some of the tissues under consideration! And with these anatomical changes Ave find besides corresponding chemical metamorphoses. As we have just said, the ground-work of con- nective-substance consists originally of protein matter or near deriva- tives of the same. A substance nearly allied to, or identical Avith, mucin (p. 21), also makes its appearance here very frequently. Almost everywhere the chemical constitution of earlier clays is missed, more remote descendants of the protein group appearing, namely, the glu- tinous substances (p. 22), and amongst them usually glutin or more rarely chondrin: local transformation of the ground-substance into elastic mate- rial (p. 23) may also take place. In the cell-body also the original proto- plasm may be replaced by other matters, such as pigments, fats, &c. ]STow, as Ave have already remarked, a classification of the tissues be- longing to this group must be looked upon as a doubtful matter, owing to the intermediate forms and transitions which are constantly en- countered. / Wo will, hoAA-ever, distinguish between—1. cartilaginous; 2. gelatinous and reticular connective-substance; 3. fatty tissues ; 4. ordi- nary connective tissue; 5. bony tissue; and, 6. dentine. ^ 5. Cartilage. §103. By cartilage Ave understand a compact tissue (appearing very early in the embryo, often rapidly maturing and as often rapidly decaying), which is widely distributed throughout the body, and formed of cells situated in an originally homogeneous intercellular substance. The specific gravity of cartilage in keeping with its solidity is considerable, amounting, according to W. Krause and Fischer, to 1-095 and 1-097 for that of the joints' and the ear. The flexibility and elasticity of cartilage is by no means inconsiderable when in thin pieces or plates; but thicker pieces are brittle, and snap easily. According to the regions in which they occur, anatomists have divided cartilages into articular, or such as clothe the extremities of TISSUES OF THE BODY. 169 bones entering into the formation of joints, and membranous, or such as serve for the formation of cavities, in that they strengthen and solidify the walls of the latter. Another classification based on the length of existence of the tissue might be said to be natural. We meet, namely, early in intra-uterine life and very Avidely distributed, a cartilaginous skeleton, the greater part of Avhich disappears in the normal process of development at an early period, being destined to give place by decay to another tissue, namely, bone, whilst only a small portion is retained throughout the whole of life. The first of these is temporary, the second permanent car- tilage (1). There is, hoAvever, a third and more rational classification, Avhich is based on the histological texture of the cartilage or that of its inter- cellular substance. The latter appears originally in all cartilages, homogeneous, transpa- rent, or slightly clouded. This transparent constitution may last the whole life through, when such cartilages are known as hyaline, and represent the typical form of the tissue (fig. 157). These may be re- cognised by the unaided eye, from their appearing in thin slices, trans- parent as Avater, Avhile in larger or thicker masses they present a bluish- Avhite or at times milky appearance. Fig. 157.—Hyaline cartilage. Fig. 158.—Reticular cartilage, from the human epiglottis. Cartilaginous tissue is, hoAvever, liable to undergo in the course of time many kinds of anatomical metamorphoses even of the inter- cellular substance, which in some cases commence very early, in others how- /| ever delay a long time in making their appearance. At one time again, they affect but small portions of a cartil- age, and at another extend themselves over the Avhole of the latter. If they appear early and spread throughout Avhole cartilages, they produce special modifications ofthe latter and are speci- ally named. Thus intercellullar substance may undergo a coarsely granular clouding, Fig- iso. or become streaky and banded, or be transformed into fibres of various kinds. At one time we perceive a partial change into parallel bands and fibres unacted on by acetic acid; at another, meet with an interlacing of dark elastic fibres, or remark in the matrix the characteristic, delicate 170 MANUAL OF HISTOLOGY. fibrillar of connective tissue paling under the action of this reagent. The tAvo last-named varieties have given rise to the distinction betAveen the elastic or reticular cartilages (fig. 158), and the connective tissue or fibro cartilage (fig. 159). Parts which have undergone metamorphoses of the intercellular substance of this kind lose the bluish-white appearance of hyaline cartilage, and become opaque and either yelloAV or white. Remarks.—Correctly speaking, this division is not good, in that we are unable to draw any distinct line between permanent and temporary cartilage, and the ques- tion is only as to differences of degree. Comparative anatomy teaches likewise that the temporary cartilages of one group of animals may be permanent in another, and vice versa. Finally, it is very frequently the case that late in life bony growths are formed at the expense of the so-called permanent cartilage. § 104. The cells of cartilage manifest no less an inclination to change than the intercellular substance. And though in very young tissue these elements present nothing very striking in their appearance, yet they may become very characteristic structures through subsequent transfor- mation. In its rudimentary condition growing cartilage presents itself as a simple aggregation of nucleated formative cells (flattened somewhat where they are in contact Avith one another), between which close scrutiny enables us to detect thin streaks of a homogeneous glistening substance. This con- dition remains throughout life among the cartilages of loAver animals. Soon after this these streaks become broader, and Avithin a short time the interstitial matter may attain proportions as great as represented in fig. 160. The cartilage cells now appear round, oval, or more or less crescentic in form, and frequently very strongly flattened. Their dimensions, exclusive of extreme cases, may he stated at 00182-0*0275 mm. The body of the cell consists frequently of a homogeneous or delicately granular proto- plasm without a membrane, and in it we almost always find a simple vesicular nucleus, measuring from 0-0075 to 0-0144. According to Rollett, this protoplasm becomes clouded in a peculiar manner on being heated up to 73-75° C. Under the action of reagents, and even of Avater, the body of the cells of many cartilages may be seen to assume jagged or stellate forms. Violent Kie. leo-Ceils of an cm- electric discharges also cause the cells in question bryonic temporary car- ' , , , , ° . nuwwuu Wage from the pig. to take on the same forms, Avith a simultaneous de- crease in size (Heidenhain, Rollett). They are also probably endoAved Avith vital contractility; but this has not yet been proved beyond doubt. The further changes to which the cell (fig. 161) is liable apply less to the shape (Avhich generally remains one of those mentioned) than to the size, Avhich increases, and at times to a very great extent. The nuclei also frequently lose their vesicular nature, becoming solid Avhile they re- main smooth, or else assuming a granular appearance. Deposition of fats in the body of the cell may also commence early. Another appearance, Avhich is remarked not unfrequently in many mature cartilages, though to a variable extent, is also of great significance. Halos or rings of a sometimes homogeneous, sometimes laminated, sub- TISSUES OF THE BODY. 171 Fig. 161. —Diagram, of well-deve- loped old hyaline cartilage, with various kinds of cells. stance, surround isolated cells or groups of the same, at one time very distinct, at another blending in their periphe- ral portions into the matrix (fig. 161). These are the long-known cartilage-capsules, Avhich we have already considered in a former part of our work (p. 87). We are here met by the important ques- tions: how have these capsules originated? Avhat is their relation to the cell and inter- cellular substance 1 and what is the source of the latter? The opinions of histologists on the points in question have varied from the earliest days of microscopy in the most marked way. It was long ago supposed, under the belief in the spontaneous generation of cells and the doctrine of blastema, that the intermediate substance was gradually insinuated between the cells (§ 102), and that the cartilage-capsule Avas formed of a modified layer of the latter around the cell: consequently, that the capsule Avas deposited externally upon the cell-body. On the other hand, some, while they allowed the origin of the apparently homogeneous intercellular substance to be that just stated, still looked upon the cartilage capsule as a product of secre- tion from the cell, fusing at its periphery Avith the matrix. According to a third view (1), the capsule, as well as the intercellular substance, is a material supplied by the cartilage cells. But it is still a subject of con- troversy whether the capsule and groundmass are to be looked upon as a secretion of the cells, Avhich has become solid, or a part of the body of the latter, Avhich has undergone metamorphosis; or, again, Avhether, as a rule, this intercellular matter is to be considered structureless or the reverse. The last of these three views is, in our opinion, the only one tenable at the present day (2). We are able, indeed, by means of certain reagents, to demonstrate with complete certainty that the so-called intercellular substance of many car- tilages is only apparently structureless (fig. 162). This is seen to be the case in the frog, Avhile it is less distinctly evident and more difficult of demon- stration among mammals. It is, in fact, by a process of repeated formation of capsules that the matrix is produced and increased in quantity. The Avhole ground-work of cartilage consists of nothing but a number of large systems of capsules, which have become fused into one another. Each car- tilage cell, therefore, takes a part in this process. In many cases these concentric laminae in the cap- sule appear in section of exactly the same refrac- tive poAver, and consequently it was formerly sup- posed that the intercellular substance of cartilage Avas homogeneous and structureless. But if, on the other hand, the youngest layers in the system presents different optical bearings (which occurs, as we know, not unfrequently), the term cartilage - capsule is usually applied to them. But although so much is, in our opinion, certain, yet the problem as to whether these capsules are the products of secretion of the cell-body Fig. 162.—Thyroid cartilage from the piR, after treat- ment wih chlorate of pot- ash and nitric acid, showing the intermediate substance resolved into the portions belonging to each cell. 172 MANUAL OF HISTOLOGY or are the transformed outer portion of the latter, is not yet capable of solution, in the present state of our knoAvledge. We are inclined, hoAV- ever, with others, to give the preference to tho latter view. Remarks.—1. There are, besides, instances in which this origin of the intercellular matter may be recognised Avithout any trouble. As Remak has very correctly shown, the xiphoid process of the rabbit affords a suitable object. Here the cells may be seen surrounded by broad halos.—2. Remak may, to a certain extent, be numbered among these. The observations of Heidenhain also are of importance. He succeeded, with the help of warm water, and the action of potash with nitric acid, in resolving the structure of the apparently homogeneous intercellular substance of frog's cartil- age. I myself have arriA'ed at the same result on repeating the experiment. §105. The segmentation of its cells, or, as the usual expression is, endogeneous cell-formation (fig. 163), is no less characteristic of cartilage. This pro- cess has already been described in § 55 : we refer the reader to what was there stated. We mentioned there also that all the phases of this process of segmentation had not yet been placed beyond doubt by obser- vation. Thus We still require satisfactory proofs of stages 2, 3, 5, and 6 Avhich have not yet been observed, owing perhaps to the rapidity of the process. As we have already seen, two (7), four (8), or indeed Avhole generations of so-called daughter-cells (9), may lie in the interior of a capsule. In the costal cartilages of elderly indi- viduals, we have the best oppor- tunity of observing these latter very much enlarged, and con- stituting the so-called mother or parent cells: they may at- tain a diameter of from 0-113 to 0-226 mm. These again may enclose Avhole swarms of daughter-cells. The forma- tion of laminated envelopes may then take place subse- quently on the daughter-cells Avhich have sprung up Avithin the original capsule (8, 9), and these may appear in course of time to lie free in the tissue (after that the parent capsule has become fused Avith the ground-substance) undergoing probably later on the same process of segmentation over comes very rich in cells, .howfcg the i»raa^™d^SX& cation plays m the formation of the latter tissue munipn This explains the fact that growing cartilages, in which no kind of regeneration of cells can be discovered, nevertheless acquire gradually a lat number of cartilage elements. And, in fact, on searching tLo74 cartfhl issue we frequently meet with spots where the cells 8KZS though jammed against one another, and flattened at the point of contact Fitr. 163.—Cartilage-cells engaged in the act of segmenta- tion (so-called endogenous multiplication), a, body of the cell; 6, capsule; c. nucleus; d, endogenous cells■ e subsequent formation of capsules on tho. exterior of the latter; g, external portion of the capsule, which fuses with ground-substance of the cartilage. Diagrammatic TISSUES OF THE BODY. 173 (fig. 161), and Avhose partial origin in the manner just mentioned is at least very probable. In many cartilages besides, Avhich are on their way to dissolution, and where a lively change of tissue is commencing again, there often occurs a very extensive segmentation of ceUs. This is especially the case where in the foetus the production of bone begins at the expense of, and together Avith, softening of the cartilages. It Avas formerly sup- posed that other tissue elements (medullary cartilage cells), 'allied to lym- phoid corpuscles, could spring from the daughter-cells. These Avere then believed to take part in the formation of other tissues, such as' the bony, fatty, and connective. We shall refer again to this in dealing with osteo- genesis. §106. The nature of cartilage, as that of a very early formed and rapidly- senescent tissue, explains the fact that, in examining, not alone the mature or aged body, but also the foetal in part, Ave encounter a series of changes in the tissue in question, Avhich, occurring more rarely in other parts, are usually looked upon there as pathological occurrences, but Avhich may here be set down for the greater part as normal processes, and must, therefore, be discussed here. The transformations Avhich may affect the cell and ground-substance in various Avays are more especially three—-fatty infiltration, calcification, and softening. They occur principally, but not exclusively, in hyaline cartilage. Fatty deposit may commence, as, for instance, in the human costal cartil- ages, even in infancy (fig. 164 a, b). We first remark very small isolated globules of oil, which either lie separately in the body of the cell or grouped around the nucleus. On their becoming more numerous, they coalesce, forming drops of greater magnitude, Avhich either lie in the cavity of the cell, without order, or, more frequently still, they so envelope the nucleus that it cannot be recognised with- out the aid of reagents. Thus it was that that vicAv,held by earlier authors, originated, namely, that the nucleus could itself be transformed into an oil-globule. Should the process advance very far, almost the whole cavity of the cell may eventually be occupied by one large drop of oil, or a swarm of globules. Calcification of cartilagi- nous tissue is essentially different from true OSsifica- Flg 164_Co«tal cartilage of an infant, transversely cut. tion, that is, from the for- a, a Wt'ion from the circumference; b, from the interior. mation of genuine bony sub- stance containing peculiar cells, although both processes were formcily confounded Avith one another. 174 MANUAL OF HISTOLOGY. We now know that cartilage hardly ever becomes bony tissue, but on being calcified, it has rather attained the end of its course and neither grows nor is further developed in any other manner. In this form it may exist for a longer or shorter period, and, in many of the lower animals, the whole life through, or, more frequently still, it may undergo a rapid re-solu- tion, in order to make way for the formation of true osseous tissue We are indebted to Bruch, but more even to //. Muller, for having first enlightened us as'to the right way of viewing these processes. In some rare cases it is the cells (a-e) which are first affected by calcifica- tion (fig. 165), but more commonly the ground- mass (/). Later on, we see both parts equally at- tacked by it, or perhaps the process may con- fine itself principally to the intercellular sub- stance. This process consists in the deposit of either finely granular, or, Avhat is more rare, of coarser crumbs and mole- cules of the salts of lime. The tissue becomes, owing to this, more and more opaque, until, finally, it is so in an extreme degree. Touching the cartilage- cells, those Avhose cap- sules are apparent, still as well as those where the latter have been merged into the ground-sub- stance, may become the seat of the deposition of lime-salts. Thinly cap- suled cells show us the molecules more on the interior of the enve- lope, or perhaps in its cavity also (e). If the capsule be stronger (a, b, c), it is impregnated with calcareous salts, while the real cell usually remains soft. When daughter-cells are present (g, above), Ave frequently remark, beside the calcification of the parent-capsule, a deposit of salts in the layers of the secondary envelopes. If the deposition take place regularly in the ground-substance, the granules of lime are (especially at first) arranged in groups around the cells (fig. 165, g, beloAv, and 166, a). Later on their amount increases more and more in the rest of the matrix (fig. 166, ?>, c, d) until at last they may appear heaped up, molecule on molecule, in the closest cuntact with one another (fig. 165,/). This calcification of cartilaginous tissue occurs in the first place to a very great extent in the embyronic and earlier periods of life, appearing there in the falsely-called ossification of cartilage. Cartilage of this kind soon becomes dissolved. On the other hand, this same process appears subsequently as an ordi- nary occurrence in the so-called permanent cartilage of later life; for in- stance in that of the ribs and larynx. Calcified masses of the last kind Kig. 165.—Diagrammatic sketch of calcified cartilage, a, A cap- sule with thick walls and shrivelled contenrs; 6, another, with d lUghter-cells; c, with very thick walls; d, very markedly calci- fied ; e, cell with a thin membrane undergoing calcification; /, a piece of cartilage with molecules of lime between and around the cells; g. another, in which the granules surround the cell more completely. TISSUES OF THE BODY. 175 further progress, and forming cavities into which the cartilage cells or their descendants find entrance. In consequence of this process of liquefaction, a system of canals may be formed, which may either open externally towards the perichondrium, or enter into communication Avith the passages of a neighbouring portion of bone containing vessels, which soon make their Avay into the interior of the cartilage, and may be recognised there. In the mass which fills up these sinuses in the cartilage, Ave have the before-mentioned medullary cells (p. 171). The process of liquefaction of a portion of already calcified cartilage- tissue is of a precisely similar kind. § 107. In inquiring noAv into the mode of occurrence of the several varieties of cartilage, the folloAving facts as regards the human body may be remem- bered. Hyaline cartilaginous matter (partially fibrous, softened, or calcified, however, after a certain age) forms the rudimentary skeleton in the foetus, that is, the several portions of the vertebral column, of the thorax (not ex- cepting the clavicle), of the shoulders, of the pelvic bones, and in addition, many of those of the head. In the adult this hyaline texture remains in the cartilages, clothing the ends of the bones entering into the formation of arti- culations (Avith the single exception of the maxillary). It remains in the car- tilages of the nose, and the larger ones of the larynx, namely, the thyroid 176 MANUAL OF HISTOLOGY. and cricoid, but only partly in the c. arytenoidea. Again, in the half rings of the trachea and bronchi, as well as in the costal cartilages, and ensi- form process of the sternum. Finally, in the symphyses, and equivalent ligamenta intervertebralia, a thin layer immediately in contact with the bone is to be found, which consists of genuine cartilaginous matter Avith homogenous intercellular substance. Of the numerous parts formed of this tissue some deserve special notice. The rudimentary cartilaginous skeleton of the foetus presents at first small roundish simple cells, closely crowded together, with vesicular nuclei, and situated in a scanty soft ground-substance. Should such a cartilage have reached an age at which it is about to fall a prey to advancing ossification, the intercellular matter is seen to have consider- ably incieased. The cells have also increased in size, especially towards the line of commencing ossification, at the same time that their capsules cannot be said to have become thickened. Endogenous multiplication has produced here a large increase also in their number. The daughter cells so formed are noAv, as the saying is, free, in that the capsule of the parent-cell is merged into the ground-substance, which is either homo- geneous, fibrous, or streaky. They now lie either in long rows one after another, frequently compressed into an obliquely oval form, as in the middle portion of a groAving holloAV bone (in the so-called " direction " of cartilage-cells), or they appear in irregular groups, as in the epiphyses and short bones. The cartilage has now become vascular besides. ■ Articular cartilages are thin coArerings for the ends of bones entering into the formation of joints. When firmly united to the bone at their under surface, they represent the remainder of the original rudimentary car- tilage, Avhich has not given way to the encroachments of ossification. Their superficial portions, lying free in the cavity of the joint, contain small but strongly flattened cartilage cells measuring 00113-0-0178 mm., croAvded one over the other, in a Avay that reminds us (when seen in vertical sec- tion) someAvhat of laminated epithelium. Further doAvn, or at a greater depth, Ave see the cells in the groAving substance separated somewhat more widely from one another. They lose at the same time the flat- tened appearance, becoming taller and larger, increasing to 00156- 0-0282 mm. and upwards, with nuclei of from 0-0065-0-0090 mm. At first they are piled Avithout arrangement in heaps over one another; hut deeper in the vicinity of the bone, they group themselves into long rows, perpendicular to the surface of the latter. The remainder is made up of beds of calcified matter. In the large cells of articular cartilage, daughter- cells are frequently present, while fatty globules are occasionally, but rarely met with. The costal cartilages have been frequently described by histologists as the best examples of hyaline structure, but incorrectly so on account of their various transformations. In the neAV-born infant there appear in a com- pletely homogeneous ground-substance (fig. 167) beds (a) of small cells (parallel with the surface) like rents in the matrix, Avhich have a delicate outline, and which contain nuclei of about 00056 mm. in diameter. The length of these cells is 0-0095-0-0150 mm. Their contents are either quite transparent or dotted with a few very minute oil-globules of about 0-0018 mm., or even less in diameter. More internally we encounter a number of generally narroAv oval cells, some- times reniform or wedge-shaped, placed in every position as regards one another, whde in the deepest portions of the costal cartilages, the largest and TISSUES OF THE BODY. 177 broadest cells (b) are to be found, some of oval or spherical form and diameter of 00169-00282 _— -~0-----j .------ o, internal portion. stiff, croAvded bundles of fibres running parallel Avith one another, and becoming lost in the neigh- bouring ground-mass. These do not pale on treatment with acetic acid. Again, in many localities the intercellular substance appears granular and clouded, in others cleft or further split up into bundles (b). Here also, in transverse sections, Ave meet Avith small flattened cartilage cells, close under the surface, arranged in several layers, and Avithout any capsules or so-called daughter-cells. They lie in the usual manner Avith their long axis parallel to the edge of the cartilage. Deeper doAvn the cells, Avhich are still in general of but small dimensions, take up an irre- gular position, becoming gradually broader and larger. We may meet with some toAvards the centre, measuring 00750-0-1150 mm. At the same time, the position ofthe elements either remains irregular, or they may be more or less arranged in radiating lines. Here Ave find the daughter- cells also more numerous (d, e, f). The cells found in the portions Avhich have become fibrous may be enormously large, attaining in some cases a diameter of 0T423-0-2256 mm. They are of roundish, oval, or elongated form, Avith whole swarms of endogenous cells, 20, 25, or 30, or even 60, as Donders once saw. Capsules are of very ordinary occurrence around the cells in the more internal portions of the costal cartilages. They are of varying but gene- rally considerable thickness (/), and appear at one time distinctly marked off externally, at another blending into the surrounding ground-substance. In other cartilage cells this capsule system cannot be distinguished opti- cally from the surrounding matrix (d), or has developed into fibres (e). * The large amount of fat Avhich (commencing at birth) has been gradu- ally accumulated here, is also Arery remarkable. Here may be seen larger or smaller globules, Avhich coalescing—especially in the neighbour- hood of the nucleus—may frequently envelope the latter, so that Ave haA-e apparently to do Avith a drop of oil in its place. 178 MANUAL OF HISTOLOGY. Again, processes of liquefaction and calcification, as well as incjPiellt ossification, are of common occurrence in the costal cartilages of elderly individuals. Noav, concerning the hyaline cartilages of the larynx, Ave observe in the larger ones, namely, in the thyroid and cricoid, many layers of small and narrow flattened cells, immediately beneath the perichondrium, lying in a homogeneous, or occasionally streaky intercellular substance, accord- ing to the direction of the cells. The innermost layers, containing daughter-cells, on the other hand, present large and distinct cartilage cells with thickened walls. In older Fig. 168—Transverse section of the costal cartilage of an old man. a, homogeneous ground-sub- stance, which has become striated at 6, and has broken into fibres at <•; cartilage-cells may also be seen, possessing for the most part thickened capsules. At d and e, two large parent-cells with nume- rous offspring; another at/, with well-developed laminae in the capsule. subjects the intermediate matter may be fibrous or banded; deposit of fats in the cells is also of frequent occurrence here. Between these two portions, again, is situated a thin layer of larger cells, Avhose intermediate substance appears granularly clouded (Rheiner). Calcified portions, with finely granular calcareous matter, are also very commonly met with in older individuals ; and true ossification is also seen. The half rings of the trachea correspond with these two cartilages in all essential particulars of texture. The texture of the arytenoid cartilages is of great interest, constitut- ing as it does an intermediate form between that just mentioned and TISSUES OF THE BODY. 179 elastic cartilage. In some parts, namely, these are homogeneous, and then in others again the intercellular substance is traversed by elastic fibres. The latter may be seen in the processus vocalic, and at times in the tips. § 108. Elastic, reticular or fibro-reticular cartilages (fig. 169), which are remarkable for their rather yelloAvish tint and great opacity, spring from the hyaline cartilage of the foetal body. The development of their elastic fibrillation reminds us thus of the formation of the chondrin- yielding fibres of hyaline cartilage. It must be remembered, however, that it is a process which belongs to the earlier periods of life, whilst the appearance of fibres containing chondrin is an occurrence of a later time. In young bodies the originally homogeneous constitution of the cartilage may remain at particular points, especially in the vicinity of some of Fig. 169.—Reticular cartilage from the ear of the calf, a, cells; 6, intercellular substance; c, clastic fibres of the latter. Fig. 170.—Fibro-reticular carti- lage from the human epiglot- tis. the cartilage cells. The fibres are at one time thin and delicate, at another dark and irregularly bordered, with a very intricate course, reti- culated or tangled like the fibres of felt. Wherever this fibrillation is very strongly pronounced, the cells may be concealed to a great extent, as, for instance, in the epiglottis (fig. 170), and pinna of the human ear. The proportion of intercellular substance to the cells is also subject to great variation, to such an extent at times that the latter may in one instance be separated from one another only by narrow belts, or, on the other hand, by a large quantity of interposed matter. The fibres are those belonging to the elastic series, Avith the characteristic power of resisting the action of reagents. They take their rise through an immediate meta- morphosis of the homogeneous blastema without the intervention of cells, as is indicated by the fact that in the human arytenoid cartilages the homogeneous ground-substance is immediately continuous with the fibrous. The cells of reticular cartilage, which vary greatly as to form and size, are easier of isolation than those of the hyaline tissue. They are usually scattered Avithout any definite arrangement, although we may find in the peripheral portions of the epiglottis small narrow elements, as in perma- nent hyaline cartilage. The cells of reticular cartilage, farther, are often remarkable for possessing less definite capsules and a less marked ten- dency to the production of daughter-cells. The nuclei, Avhich are either smooth (in Avhich case they contain a nucleolus), or granular, occur there- fore single as a rule, or more rarely in pairs. In the body of the cell or round about the nucleus fat may also be met Avith here. 180 MANUAL OF HISTOLOGY. Among the cartilages of the human body which have a thoroughly solid reticular intercellular substance, may be numbered certain portions of the respiratory apparatus, namely, the epiglottis, the cartilages of Wrisberq and Santorini, the Eustachian tube and pinna of the ear. Further, as having a partially fibrous blastema, the arytenoid cartdages and intervertebral ligaments. §109. We have now to enter on the consideration of a third species of this tissue, namely, of the connective-tissue cartilage, or, as it has been less happily termed, fibro-cartilage (fig. 171). This may be looked upon as a hyaline cartilage whose abundant matrix has developed into fasci- culi of connective-tissue, or as a solid species of the latter, through which cartilage cells are scattered. The fact is that it is usually a mixture of connective-tissue and cartilage. Like connective-tissue, it contains elastic fibres as Avell as the cells of this tissue, known as con- nective-tissue corpuscles. BetAveen the latter and many cartilage cells there occur intermediate forms, so that fibro-cartilage may pass into ordinary connective-tissue without any line of demarcation, especially at those points at which it becomes poor in cells. On the other hand, its bearing as a cartilage, Avith connective-tissue matrix, appears clearly in the intervertebral liga- ments, Avhere Ave find close to portions which are hyaline in texture other points Avhere the matrix is obscurely fibrous, and continuous with a substance which is evi- dently, connective-tissue. Fibro-cartilage, which is brought espe- cially into use in the construction of joints, appears to the unaided eye of Avhitish or slightly yellow colour, and to possess a texture sometimes solid and sometimes rather soft. It is more exten- sible, further, than ordinary cartilage. Under the microscope we find, instead of the homogeneous matrix of hyaline cartilage, connective-tissue with fibres sometimes more indistinct than at other times, when they may be very sharply defined. The bundles are usually crossed in all direc- tions confusedly. They may, however, preserve some definite direction on the other hand, while their optical and chemical bearing is quite that of ordinary connective-tissue (see below). As to the cartilage cells, their proportion is in general but small, and frequently, indeed, very incon- siderable, so that they require to be searched for. The size, further, of the cells is also small, and their whole constitution simple, the out- line being usually very delicate, and the nucleus, as a rule, single. Cells with two nuclei are rare, and those containing daughter-cells apparently do not occur at all. Fatty infiltration likewise, Avhich is so common in other species of cartilage, is here of rare occurrence. The position of the cells is also liable to variation. They are either Avithout arrange- ment or crowded together in small groups, or again, arranged one after another in rows. The latter position corresponds with the direction of the fibres of the tissue. Fig. 171.—Fibro-cartilage from a human Ligamentum intervertebral (half diagrammatic). TISSUES OF THE BODY. 181 Connective-tissue cartilages possess vessels, but only in smad num- ber ; but as to the presence of nerves, we are as yet unable to state any- thing certain. Among them the cartilages of the eye-lids may be reckoned, of which the upper appears to be richer in cells than the loAver, Avhich has but &av of the latter (Gerlach); further, the c. ti-iticece of the larynx, which may, hoAvever, consist of hya- line substance (Rheiner); then the c. inter- articulares, as Avell as the so-called labra cartilaginea of certain joints, with the car- tilaginous knots found in tendons. As a rule, it seems to be part of the composite character of the fibro-cartilages, that struc- tures formed of pure connective-tissue may be transformed at points into the varieties of the tissue in question by the imbedding of cartilage cells. This is the case in the terminal portions of tendons where they are inserted into bone, as well as many parts of their sheaths (Kblliker). Finallv, fibro-cartilage, springing, moreover, continuously from the hyaline, 'appears in the symphyses and so-called half-joints, which have their origin in the liquefaction of the central portion of solid masses con- necting bones (Luschka). Among the latter, those most Avorthy of consideration are the sym- Fig. 172.—Diagram of a vertebral symphysis divided vertically. At a, the pulpy centre; at 6, the fibrous ring; at c, the cartilagin- ous covering of the body of the vertebra; d, the periosteum. Fig 173 —Vertical section through the bodies, the last dorsal and first lumbar vertebra of a human embryo at ten weeks. Body with calcified carti- laginous tissue, a; and unchanged, 6; at c the fibrous ring developing, con- sisting of elongated cells (?), and with a cavity containing transparent cells at d, which becomes the pulpy nucleus of the infant physes ofthe vertebra, so frequently the subject of investigation, the so- called ligamenta interoertebralia, about which Luschka has imparted to us such valuable information. They present themselves ra of a foetal pig, of bands and appearance of chondrin fibrillation occurs 2 inches in length. afc ft much ]ater ^^ Great interest attaches to the discovery made by Schwann, and after- wards confirmed by Hoppe, that the ground-substance of foetal cartilage does not consist originally of a matter yielding chondrin, or indeed of any material which stiffens, like glutin, on coolinc. All the statements just made refer, in the first place, to hyaline carti- lage : the primary form of reticular and of fibro-cartilage, however is also included. The latter consist originally also of a homogeneous ground- substance, in which the metamorphosis into fibres commences sooner or later, and continues in some parts even after birth. TISSUES OF THE BODY. 187 Fig. 176.—Gelatinous tissue with roundish cells from the vitreous humour of a human foetal eye. 6 and 7. Gelatinous and Reticular Connective-Substance. § H3. Under the name of gelatinous or mucoid tissue and reticular connec- tive-substance combined, we shall noAv consider a second series of tissues, liable to great variation, and belonging to the group of connective-sub- stances. This classification, hoAvever, can only be said to have a provi- sional value : it remains for more accurate histogenic investigation to shoAv, at some future time, whether the mode of development of the different tissues placed together here justifies or modifies our method of arrangement. Gelatinous and reticular connective-substance appear at the first glance separated by a wide gap from car- tilage. Whilst in the latter we have to deal with a tissue made up of round cells held together by a solid glutinous intermediate matter, the plan of the tissues with which we are now engaged is completely different. They are all of them more or less soft, partly swollen up into a glutinous condi- tion, or in other rarer cases even present themselves in the liquid form. Onlyin exceptional cases do their cells preserve their spherical form: they present themselves, as a rule, in most character- istic figures, radiated and stellate, and united with each other by means of simple or branched pro- cesses, forming networks of cells (figs. 177 and 178). The system of meshes so formed varies as to its contents very considerably, apart from the differences in the size of its meshes. In a certain number of the tissues which may be reckoned in this category, the net- Avork formed by these elements is occupied by a structureless, watery jelly, containing mucin or some allied substance, when we term it a gelatinous or mucoid tissue (fig. 177). A second and more extensive group shows us these interstices, instead of being occupied by a mucoid mass, filled rather with innumerable granular cells, which correspond exactly with the elements of lymph. We have thus pre sented to us the most Avidely distributed species of reticular connective-substance (fig. 178). It has been named "cytogenous connective-sub- stance " by Kblliker, and by His " adenoid sub- stance." Another series of connective matters belonging also to this group in our opinion, encloses, in a usually narrow-meshed and delicate cellular net- work, another kind of contents, e.g. chiefly, ner- vous elements (fig. 179), or also, though much more rarely, masses of Fig. 177.—Gelatinous tissue with stellate cells, from the enamel- organ of the human embryo. 188 MANUAL OF HISTOLOGY. fat. This may be designated for the present as ^ftacula\^Z matter, and is a species which has, up to the present, been investigated * The fibrous character of most of the tissues enumerated here is by no Fig. 178.—Reticular connective-substance with lymph corpuscles from Peyer's follicle of the adult rabbit, a, capillaries; 6, reticular frame- work; c, lymph cells (most of the latter have been removed by brushing). means lost, however; for Ave frequently see, Avhether in the course of physiological development or as a pathological occurrence, many of these tissues, the mucoid as well as the reticular, becoming transformed into ordinary fibrous tissue, in that the cellular network obtains coatings of filaments Avhile the gelatinous intercellular matters, or as the case may be, lymphoid corpuscles, decrease and finally dis- appear. Then, again, Ave recognise that other substitu- tion already mentioned section 101, in different groups of animals. Thus, for instance, the reti- cular connective-substance in one organ of certain animals is replaced by ordinary fibrillated connective-tissue in other species, and so on. Finally, it seems probable that any of the other tissues belonging to this so widely distributed connective-substance group are all capable more or less of reproducing from their cellular offspring either mucoid or reticular tissue. §114. We have just seen that by gelatinous or mucoid tissue is understood a cellular structure, characterised by possessing a very soft and Avatery intercellular substance, containing either mucin or some matter very Fig. 179.—Sustentacular tissue from the poste- rior column of the human spinal cord. TISSUES OF THE BODY. 189 similar to it, and which is thus distinguished from glutin-yieldinc car- tilage and regular connective-tissue. The amount of this interstitial substance is usually considerable, so that all the physical properties of the tissue are determined by it. In this respect cartilage and gelatinous tissue resemble each other, though, on the other hand, they may differ Avidely as regards consistence. The cells in a soft interstitial substance of this kind are originally of spheroidal figure, and Avhen imbedded in a completely homogeneous mass may be regarded as the simplest form of gelatinous tissue—one Avhich is, hoAvever, but extremely rarely permanent, and which is destined to undergo, as a rule, further transformation. The cells, in such cases, are metamorphosed into fusiform and stellate structures, displaying a strong inclination to unite with one another, and in the intercellular substance there commences to make its appearance a streaki- ness and fibrillation. In general, mucoid tissue may be said to be a species of connective- substance standing Ioav in the group, and as such it enters into the com- position of temporary embryonic structures under normal conditions, which do not attain in this form a state of maturity. In fact, AA'e have to do Avith foetal tissues. The cells further, Avhile still in their simplest form, may be so compressed by the superabundant interstitial matter that they cease to exist, the latter only remaining over. It is, Iioav- ever, more usual to meet Avith an ascending metamorphosis in other of these textures, by Avhich they are developed into ordinary soft connec- tive-tissue. The points of distinction, consequently, between the two cannot be very definitely laid doAvn. The parts of the human body Avhich are looked upon at the present day as belonging to this group of tissues are the folloAving:—the vit- reous humour of the eye; the gelatin of Wharton of an early period of life; certain substances filling up the interior of the rudimentary ear; the enamel organ of the rudimentary teeth; and the soft, formless con- nective-tissue of intra-uterine life, which has not yet developed collagen. But in animals gelatinous tissue is more permanent. Thus the sinus rhomboidalis in the spinal cord of birds is formed of it, and the form- less connective-matter of fishes. It appears also Avidely distributed among the lower animals. The bodies of the acalephse are chiefly made up of it (Virchow and Schultze). Whilst in the mature body no gelatinous tissue is to be found, Avith the exception of that small quantity known as the vitreous humour, it may be produced anew under abnormal conditions by development from another member of the group of connective-tissues, as, for instance, from fatty tissue in cases of emaciation. Tumours formed of mucoid tissue are knoAvn as myxomas ( Virchow). §115. The simplest form of this gelatinous tissue to be found is in the corpus • vitreum of the eyes of embryos and very young individuals. The surface of the latter is originally covered Avith a vascular net- work, Avhich is obliterated, however, very early. If Ave examine the structure in a foetus at about the end of the fourth month (fig. 180), we find it to consist of au abundant and completely colourless, homo- geneous, and somewhat viscid ground-substance, Avhich becomes stringy on the addition of acetic acid. In this are imbedded, at tolerably 190 MANUAL OF HISTOLOGY. regular intervals, a rather scanty proportion of cells, either quite spherical orspheroidal, which may take on other distorted forms, however, owing to their soft consistence and the semi-fluid nature of the surrounding medium. They resemble enlarged colourless lymphoid cells, &c, and are granular, either coarsely or finely so, but usually to no great extent, so that they are not very opaque. Their membrane opposes a certain amount of resistance to the action of acetic acid, and the nucleus appears more or less granular, showing in its interior a nucleolus. We also meet with, round, oval, reniform, and double nuclei, which have always their special nucleoli, indicating probably a multiplication of cells here. The size of these cells is 0-0104, 00156-0-0182 mm., while the simple nuclei have an average diameter of 0-0052 mm. Fusiform and stellate cells are not entirely absent in the true corpus vitreum, but are found principally in the membrana hya- loidea in connection Avith the for- mation of the vessels of that part, as Kblliker j ustly observes. The same is found to be the struc- ture of the vitreous humour of the infant, while, according to the general opinion, the cells undergo decay in the first years of childhood, so that in adults the corpus vitreum is composed of the intercellular substance alone; a vieAv which is opposed by O. Weber. According to this observer, namely, the cells of the mucoid substance remain in all cases, though more scanty towards the centre than at the periphery. Examined chemically by Berzelius, Lohmeyer, and Virchow, the corpus vitreum Avas found to contain more than 98-5 per cent, of water, and among the solid constituents an abundance of inorganic matter, chiefly made up of chloride of sodium. Among the organic matters Ave find traces of albumen. According to Virchow a substance allied to mucus is also to be found here, to which the semi-fluid gelatinous nature of the structure is due. The vitreous humour is now regarded as composed of a certain quantity of mucin gelatinised in a large amount of saline fluid. The following analysis by Lohmeyer is given for the purpose of showing more clearly the composition of the substance in question. 1000 parts of vitreous humour contain :— Fig. 180.—Structure of vitreous humour in a four months' foetus. Water, ....... 986-400 Membranes, ...... 0-210 Albuminate of sodium (and mucin 1) 1-360 Fats, ....... 0-016 Extractives, ...... 3-208 Chloride of sodium, .... 7-757 Chloride of potassium, .... 0-605 Sulphate of potassium, . . . 0-148 Phosphate of calcium, .... 0101 Phosphate of magnesium, 0-032 Phosphate of iron, ..... 0-026 Lime earths, ...... 0133 Mucin was not looked for, but urea was found by Millon and Wbhler but not by Lohmeyer. TISSUES OF THE BODY. 191 The vitreous humour is the most posterior of the refracting media of the eye. Its refractive index is (taking Avater to be 1*3358) P3506 in the human being (Krause). If destroyed it is not regenerated. Remakes.—Besides the German literature, comp. Bowman, Lectures en the Parts, die., ofthe Eye, London, 1849, p. 100. § H6. Again we find gelatinous tissue presented to us in a higher state of development (setting aside the tissues of the membranes of the ovum), in the first place in the enamel organ, then in the gelatin of Wharton, and finally in the formless connective-substances of embryos. Here we find universally, in a transparent gelatinous substance, fusi- ng. 181.—Cells from the enamel organ of a foetus four months old. At a. small; at 6, larger and more highly developed stellate cells. Fig 182 —Tissue of the gelatin of Wharton In trans- verse section; from the cord of an embryo of four months, a, a net-work of branching cells; 6, conden- sation of the ground-substance forming bands; c, un- changed, roundish, formative cell. form and stellate cells, known since the days of f^^^^t with their processes a cellular net-work, and lie at first somewhat closely toget^rhu'X a while separate more widely one fromi another, a depo, ofthe condensed intercellular substance forming around them Ihus Ave have a system of reticulated bands within which the cellular net -work stilTexisL "ihe meshes enclose a soft and gelatinous mass in which niav be distinguished isolated unchanged formative cefls. ^ke subXnce, however, of which the enveloping bands are> co= d commences early to present the appearance of ^mg lon^f^Zesl streaked. This gradually becomes more evident "f^^lTconZZ fibrous condition, on which the mass is transformed into oidmaiy conneo 192 MANUAL OF HISTOLOGY. tive-tissue fibrillse. Elastic fibres make their appearance also by the trans- formation of the same substance (see below, with connective-tissue). The cells again frequently take on a more elongated, narroAved form. If the Avhole series of transformations passes over them to its conclusion, which is by no means always the case, what is known as formless connective- tissue is formed. After this general description, let us subject the enamel organ and umbilical cord to nearer examination. The first of these covers the germ of the rudimentary tooth during intra-uterine life and the earliest years of infancy. Its tissue (fig. 181) consists of delicate stellate cells Avith distinct nuclei. The latter are vesicular in the embryo of four months, measuring 0*0066- 0*0090 mm., whilst the cell Avith its processes shoAvs an extent of 0*0260- 0*0385 mm. The number of these latter is at times only four (cc), but often far greater (a, b). There occur also cells Avith double nuclei, and at times a species of segmentation is observed (b, beloAv). The interstices between the cells so united to one another attain a breadth amounting to 0*0204-0*0320 mm. and upAvards, and are filled Avith a homogeneous gela- tinous mass, Avhich gives. to the whole enamel organ the same consistence vary- ing in density according to its amount. That we have here to do with a transient tissue re- quires no farther comment after what has been just stated. It ceases to exist Avhen the enamel of the tooth attains maturity. In the mucoid substance again Avhich enters into the composition of the umbilical cord (fig. 182), namely, the gelatin of Wliarton, cells exactly similar to those encoun- tered in the enamel-organ are to be found. Bwfith^celhlar net_ with well-developed cor.nective-tissue fibrXtion a i' WOrk (%• 182, a) becomes Sed^cenl la"er Wit"tl,eir corpuscles in the axis' c' 'd- <: enveloped at a very early cately streaked intermediate substance (b), and ^^Zsystm of meshes still remaining we meet with the same structureless mucoid ely Here may be found also spherical cells (c) as they appear in the same stage o development of structureless connective-substence. They a contractile, and migrate (Koester). The bands of condensed * round matter enveloping the cellular net-work ffi, a similar membrane fenestrated at intervals. Fig. 202.—From the middle and ex- ternal coat of the aorta. 1. An clastic membrane (from the ox) fenestrated to a great extent (a), and with thick bands between the various holes, 6, c. 2. A network of broad elastic fibres from the whale, which are partly pierced with minute foramina. that, in many instances, we can only obtain by dissection short fragments of the formations in question. 210 MANUAL OF HISTOLOGY. Thus the yellow ligaments of the vertebral column are uncommonly rich in elastic fibres of 0*0056-0*0065 mm., Avhich are usually met with bent or arched, and giving off a tolerable number of branches, Avhich are also hooked or like tendrils, and frequently attain a remarkable degree of fineness. In the infant such fibres have still but a small diameter, and it is not before a certain amount of maturity of the mammal body has been attained that the formation of these broader fibres takes place. Smaller individuals only shoAV the finer examples. The amount of fibrillated connective-tissue found amongst these is subject to great variation. Though in many localities tolerably abundant, it becomes in others rather scanty, and often excessively diminished in amount. It was in such cases as this that earlier investigators Avere accustomed to speak of elastic tissue. There could hardly be a more suitable object for the study of an elastic tissue of this kind in all its peculiarities, than the walls of the larger arteries, especially those of the larger mammals. Here we meet Avith thin elastic membranes (fig. 201, a), in which is seen a network of very fine elastic fibres embedded in homogeneous intermediate matter; or this membranous ground-substance may be pierced Avith holes of various kinds (fig. 201, b), (the fenestrated tunic of Henle). We likeAvise encounter very simple elastic tunics without em- bedded fibres (fig. 202, 1), Avhich are also studded with apertures (a), the whole of the substance presenting the appearance of bands and broad irre- gular fibres (b, c). Between such and a dense in- terlacement of broad elastic fibres (fig. 202, 2), it is often difficult to distinguish Avith certainty. Those dense netAvorks which have a homogeneous inter- stitial substance, as in fig. 203, afford still better objects*. In those localities where the elastic fibres are very broad, their edges may be here and there jagged like a saw. Again they are frequently pierced with very minute holes. This is seen very gene- rally in the external coat of the aorta of the whale, where the fibres may measure 0*0056 or even 0*0075-0*0088 mm. §128. Having now made ourselves acquainted with the ordinary bearings of elastic fibres and nets, we must turn to the consideration of the limiting Fig. 203.—A very dense network of broad elas- tic fibres from the mid- dle coat of the aorta of an ox. The fibres are connected by a homo- geneous intermediate substance of a mem- branous structure. Fig. 204.-A connective-tissue bundle from the base of the human brain, treated with acetic acid. layers of many connective-tissue bundles, which ha™ e^ » ■netaerphesis into elastic substance ef Uetat'XS tla TISSUES OF THE BODY. 211 The bundles of connective-tissue which pass from the arachnoid to the larger vessels on the base of the brain (fig. 204), with other isolated fasciculi in the loose cellular tissue under the cutis and certain serous membranes, and that of tendons even, show us a very interesting example of the artificial production of figures extremely like annular or spiral elastic fibres, and which have even been taken for them. To demonstrate this, acetic acid is employed or prolonged maceration in water. In the first place we meet with fasciculi in which the elas- tic envelope is puffed out and stretched by the action of the reagent, but remains unin- jured, the consequence of which may be twofold as to appearance. Firstly, the gela- tinised substance of the con- nective-tissue may be puffed out at intervals into globules, so that annular or at times spiral indentations arise (fig. 205, 1, 2, c), or the puffing may be more one-sided, in which case the furroAvs appear clearer and more distinctly spiral (4). All these furrow- ings are characterised by their delicate outline, which is never double. Further, Ave may be- sides recognise the presence of the envelope on the cut end of a bundle (2 d), or when it has become separated from the contents, in consequence of the penetration of fluid (1 a). It frequently occurs, how- ever, that a number of trans- verse rents are produced in this elastic envelope, in conse- quence of which the substance of the connective-tissue may swell out in globules, while each portion of the envelope be- comes more and more shortened by the pressure, a contraction ensuing, Avhich is rapidly increased by the Fig 205.—Bundles of connective-tissue from rlie base of the human brain, after treatment with acetic acid. Some of them have more or less developed elastic fibres in their interior. 1. A bundle whose envelope is not torn, but obliquely wrinkled; a small portion of the latter is separated for a short distance at a. 2. A bundle with annular shrunken portions of the sheath nt a, a more strongly pronounced puffing of the sub- stance of the connective-tissue at *>, and a longer por- tion of the wrinkled envelope at c, c, from the cut end of which, at d, the conteats are protruding. 8. A bundle with annular fragments of the envelope at a, and a larger portion of the latter at b, more strongly wrinkled. 4. A smaller bundle with uninjured varicose sheath. 9965441 212 MANUAL OF HISTOLOGY. elasticity of the membrane. Thus we remark at first the fragment of tho sheath still long and transversely ribbed (3 b), but soon, and especially when from both ends of the torn sheath the contents swelling out press upon the latter, that portion of the envelope contracts into a fine narrow ring with a dark contour (2 a, 3 a); more rarely, in consequence of a spiral rent, it shrinks into a filiform structure passing round the mass with a spiral course. Did Ave not know their origin, we might look on these shrunken fragments of the envelope as fibres of a coarser kind, encircling either as rings or spirals the bundle of connective- tissue. It is an interesting fact that fibres of cotton undergo the same changes, under the action of am- monio-oxide of copper, which may here be observed in all their phases with the most perfect ease. It seems, therefore, beyond doubt that elastic mem- branes may shrink into filiform structures in conse- quence of being completely rent. We are here met by the question, Avhether something similar to this, which we have found as an artificial production, may not also occur as a normal process in many of the elastic membranes of the body,—whether, by a partial reabsorption or rending of its substance, a membrane of this kind may not be converted into a network of elastic bands and fibres, at the same time that its substance so fenestrated diminishes greatly in extent owing to elasticity. There seems, indeed, to be no doubt that netAvorks of elastic fibres or flat bands, as we meet with them in the middle coat of the greater arteries in large mammals (fig. 206), have frequently had their origin in the manner just described. It is probable also that, by the thickening of elastic membranes at particular points in folds and bands, a netAvork of elastic tissue may be formed (fig. 203). §129. We turn now to the most difficult point in this subject, to the cellular constituents, or, as they were formerly called, connective-tissue corpuscles. In them we have the most important physiological elements of the tissue under consideration. As we have already remarked, these cells are usually obscured by the fibrillar around them, and only come into view after the use of acetic acid and other strong reagents, amid the gelatinised ground- substance. But where it is possible to obtain a vieAv of the still livino* and unchanged connective-tissue corpuscle, it is very far removed in appearance from those which have been acted on by reagents. Besides the true connective-tissue cells, all the structures we are en- gaged in considering appear to contain a second element, the lymphoid cell, Avhich has migrated from the blood-vessels. The cells of connective- tissue might, therefore, be classed with propriety into fixed and wan- dering. Let us turn now to the living tissue. An excellent spot for obtaining living connective-tissue Avas pointed out not long ago by Kuhne.* this is in those thin transparent lamellae which occur between the muscles of the leg of the fro"-. In one of these (fig. 207), we may see in the extremely soft "round- Kig. 20C.—Elastic nets from the aorta. 1. An elastic fenestrated membrane from the ox; 2. A distinct net- work of broad fibres from the whale. TISSUES OF THE BODY. 213 substance, Avhich is gelatinous and transparent, first of all the fibrillas and fasciculi of the connective-tissue (/, g), as well as a network of extremely delicate elastic fibres (h). Then the expected cells (a-e) are observed though not so close together as in our plate, but at rather greater inter- vals. All of them are naked, and appear in several varieties. The most usual form in which they are met Avith is that of a delicate proto- plasmic structure in which no nucleus can be discerned, but in its place a darker spot (a). The cells in question send off several processes which may attain considerable length, and come into contact with those of neigh- bouring cells (b). By very strong magnifying power there may be seen, beside these longer processes, a large number of shorter and paler ones, Fig. 207.—A portion of living connective-tissue, cut out from between the muscles of the frog's thigh (strongly magni- fied). , peptic glands. 230 MANUAL OF HISTOLOGY. surplus to the radicals of the absorbents contained in the tissue (§ 82). Unfortunately, the amount of this fluid is too small to alloAv of oui obtaining it for chemical analysis, so that its composition still remains unknown. Conclusions as to the constitution of the normal fluid drawn from analysis of those abnormal collections met with in formless connec- tive-tissue in oedema, appear to us inadmissible. In the serous sacs and cavities likeAvise Ave meet with a very similar fluid, in varying but usually small quantity, which might be named a Avatery exudation from the intercellular fluid of the blood, containing, on analysis, albumen, extractive matters, salts, and at times also fibrin (1). Up to the present, the only fluid contents of any of the true serous sacs that have been examined, under completely normal conditions, are those of the pericardium in the case of executed criminals (Gorup- Besanez and Lehmann). The results varied. The first of these investi- gators obtained in two cases a fluid of weak alkaline reaction and yelloAvish colour. 1000 parts of pericardial fluid consist of — Water, 1. . 962*83 2. 955*13 Solid constituents, 3717 44*87 Albumen, 21*62 24*68 Fibrin, — 0*81 Extractive matters, . 8-21 12*69 Salts, 7-34 6*69 Lehmann, on the other hand, only obtained 8*79 of albumen, 093 of other organic matters, and 0*89 of mineral constituents, per thousand. For synovia (comp. p. 155). The intercellular matter of connective- tissue, together with the fasciculi of the latter, consists of a glutin-yield- ing material. The composition of the cells is, on the other hand, still enveloped in obscurity, while in the elastic elements Ave may recognise elastin. The intermediate substance of the cornea alone is an exception, in that it yields chondrin. This short notice includes all that Avas for- merly, and is to a great extent at present knoAvn of the composition of connective-tissue. In the embryonic state this tissue possesses, according to Schwann's investigations, repeated subsequently by Schlossberger, a ground mass, from which no glutin can be obtained on boiling, and Avhich appears to belong rather to the protein group. This corresponds also Avith investiga- tions made on the constitution of pathologically formed immature con- nective-tissue, so that we see a parallel between recently formed con- nective-tissue and undeveloped cartilage (§ 112). But in that the fully developed tissue, after it has been chemically cleansed, may be converted to a greater or less extent into glutin by boiling, there must take place between the embryonic period and that of maturity some transformation of the albuminoid intermediate substance into a collagenic one Of the intermediate steps Ave know nothing, and as to the manner also in which this change takes place we have at present but hypotheses to offer- for we have not as yet been able, as is well known, to effect an artificial trans- formation of the protein substances into glutin or glutinous matters The chemical constitution likewise of those undeveloped and not vet fibril- lated portions of connective-tissue already mentioned has, with the excep- TISSUES OF THE BODY. 231 tion of the cornea, remained undiscovered: the latter also in the fcetus, it appears, yields no chondrin. The ground substance of connective-tissue remains unchanged in cold Avater, alcohol, and ether, and swells up into a jelly-like mass under the action of acetic acid, which only dissolves it to a certain extent when Avarra, and after a considerable lapse of time. Potash, on the other hand, commences to dissolve it even when cold. By boiling in water this inter- cellular matter is converted into glutin (§ 15), but whether in toto is still an unsettled question. The time necessary for this is liable to variation, according to the quality of the connective-tissue on which Ave are work- ing. As to the process also by which the collagenic tissue is trans- formed into glutin, we are as much in the dark here as elsewhere. And if in the analysis of portions of connective-tissue the same results per cent, have been obtained as in the case of the glue prepared from the latter by boiling, it only speaks for the imperfection of the chemical manipulation. It is, in fact, impossible to elucidate with any degree of accuracy the constitution of this intercellular matter, in that we possess no means of separating it from the numerous form elements entangled in its substance, namely, connective-tissue corpuscles, elastic fibres, &c, without even taking into account other accidental and unessential tissue elements, such as blood-vessels, fat cells, &c. The substance cementing the fibrillae together is soluble in permanganate of potash (Rollett), 10 per cent, solutions of common salt and in baryta and lime Avater; these take up from tendinous tissue an albuminous substance giving the reactions of mucin (Rollett). The composition also of connective-tissue corpuscles is but to a small extent knoAvn, on account of our being obliged to base almost all our con- clusions on niicrochemical reactions. Their nuclei show the usual resist- ance to acetic acid, and the protoplasm—it appears in the tendon-cells ot the mature body to be reduced to a minimum—though it may become greatly changed by the action of water alone, still offers to that of acids considerable opposition. It holds out against concentrated mineral acids for a period in which the connective intermediate substance is softened into a pulp or dissolved (2). Hot solutions of potash, on the contrary, dis- solve the whole cell rapidly, and are thus of importance in the demonstra- tion and diagnosis of elastic elements. The latter only admit of nearer investigation in those parts in which they are met with in great prepon- derance, as in the ligamentum nuchas, and to this is due the slight acquaintance Ave possess Avith elastic matter in general (§ 15). Those homogeneous elastic membranes of large vessels already discussed (§ 127), as well as the structureless intermediate substance of many elastic fibrous networks, resemble in their microchemical bearing ordinary elastic fibrous tissue. The homogeneous envelopes of certain of the connective- tissue bundles appear still to consist of glutinous substance, in that they give way to the action of caustic alkaline solutions, Avhile in other instances they are decidedly composed of elastic material (comp. § 128). The transparent limiting layers of connective-tissue membranes likeAvise are liable to the same variation in composition. Descemet's membrane on the cornea is elastic, while the anterior transparent lamina of the latter and the basement membranes are of glutinous nature. These facts just stated are, however, of interest in another way. They shoAv that elastic matter represents a product of the subsequent transfor- mation of glutin-yielding intermediate substance, and, moreover, of that 16 232 MANUAL OF HISTOLOGY. form from which collagen as well as chondrigen is produced : comp. what has been already stated in regard to elastic cartdage (§ 108). Analysis of organs wholly formed of connectiAre-tissue has been undertaken comparatively rarely up to the present. The proportion of water in the tendons amounts according to Chevreul to 62*03, in the cornea to 73*94-77*82 per cent. (His). The latter has, therefore, 26*06- 22*18 of solid matters, of Avhich in one case 20*38 were converted into glutin on boiling, and 2*84 was found to be made up of organic non- glutinous substance. The latter may be referred to the corneal cells and their processes, as well as the membrane of Descemet. Together with these were found besides 0*95 per cent, of mineral constituents, of which 0*84 were soluble in water. Remarks.—1. According to A. Schmidt ••fibrinogen" is almost always one of the components of such exudations. 2. We can thus isolate connective-tissue passages with their terminal layers, and remains of cells in the interior, by means of sulphuric, hydrochloric, or nitric acids. Prolonged, boiling also in alcohol acidulated Avith hydrochloric acid, and subsequent maceration in water, leaves the protoplasm of the cells still remaining, while the interstitial substance undergoes solution, and the elastic fibres crumble up. §138. Connective-tissue forms a large part of the ordinary investing and sus- tentacular substances of the body. It connects organs Avith one another, envelopes them, and fills out interstices between them and between their divisions: it fixes parts against one another, forms passages for vessels and nerves, and cavities for collections of fat cells, &c. This so Avidely- distributed tissue, then, comes under our consideration, as regards its physical properties, mainly for the building up of our body. Loosely interlaced as regards its fasciculi, connective-tissue presents itself in the form of a yielding extensible substance. But, on the other hand, we usually encounter a more dense and intimate interweaving of its fibres, especially in formed connective-tissue; so that a greater or less degree of solidity is attained, as opposed to the extensibility of that formless species. The plentiful occurrence in it of elastic elements has also a great influence on the physical qualities of the tissue. On the other hand, we encounter structures formed of connective-tissue which play a part in the chemical processes of the system, owing to their great vascularity or abundant exudatory activity, as, for instance, the skin and mucous membranes. This depends, however, properly speaking upon the contained blood-vessels. It is usually supposed, though without sufficient data for proof, that the transformative capacities of connective-tissue in regard to the matters passing through it are in general but small. We are led to infer this by the passive part which the tissue takes in the assimilative revolutions of the body, or its slight inclination to decay, and by the poorness in vessels of many parts formed of it. This interchange of matter, however, be it great or small, is still completely veiled in obscurity as regards its nature. The fact that glycin and leucin (§ 35 and 31) are products of the artificial decomposi- tion of glutm, while elastic material yields the last of these only may give us some slight point to hold by in the present helpless state in which we find ourselves. Some years ago, from the connective-tissue theory of Danders and Virchoic, an idea sprung up that the cellular networks of its cor- TISSUES OF THE BODY. 233 puscles, supposed to be supplied Avith membranes, constituted a hollow system of canals, like that to be met with in bone, for the con- ducting of certain definite nutritive fluids through the tissue, forming thus & plasmatic circulation. Based on this view, the name of sap canali- culi was given by Koelliker to these passages. But there was no phy- siological necessity for supposing that this must be the case in connective- tissue, in that it does not occur in cartilage. Besides, the system of interstices in parts formed of connective-tissue would appear but little suited for the fulfilment of such an object, frequently stopped as they are by cells, and compressed by the intermediate substance. Communica- tions between these interspaces and the vascular systems do not occur, either Avith the blood-vesseh or lymphatics, although this erroneous doc- trine still permeates histology. The question now arises, Avhich of the elements of form are to be looked upon as physiologically the most active and important in con- nective-tissue masses 1 Here also as anatomically the decision must be in favour of the cells, so long as the latter possess even a small remnant of their body. On the other hand, connective-tissue structures, in which the cellular elements no longer exist, and where alone dense networks of elastic fibres remain, must be looked upon as tissues endoAved with a minimum amount of life ; for instance, the ligamentum nuchas. Among the transformations of senescent connective-tissue we must now bestow a few words on calcification, occurring in a simdar manner to that in cartilage, and by no means rarely. Bony tissue may likewise take the place of the former, but much more seldom by direct transition of one tissue into the other as by a neoplastic process, corresponding to that which takes place in the embryo, where the neAvly-produced bony mass takes up the place of the vanishing connective-tissue. We shall be obliged to refer again to this question in considering osseous tissue. We are noAv met by another difficult question, namely, Iioav far con- nective-tissue cells may become transformed into the elements of other tissues not belonging to this group. It appears plain that, Avith their power of vital contractility, no great distinction can be made between them and the cellular elements of unstriped muscle. And yet there have been long and indeterminable controversies as to Avhat are muscle and what connective-tissue cells in certain organs, e.g., the lymph glands and the ovary. We have already stated (§ 98) that the so-called endo- thelia must take rise from the cellular elements of connective-tissue. On the other hand, there appears to be no transition into the cells and offspring of the corneous and intestinal glandular plates, and there seems further (if we except the neuroglia and many portions of the higher organs of sense) to be no true connection between these tissues. It is true that such intercommunication has been frequently asserted to take place, as, for instance, in the intestinal villi by Heidenhain. Here long processes of the cylinder-epithelial cells are stated to be united with those of the connective-tissue corpuscles of the sustentacular sub- stance of the villus. These statements have not, however, been corrobo- rated. The contractile and wandering lymphoid cells of connectiVe-tissue have been already dealt with in a former section. That they generally take their rise from the derivatives of the middle germinal plate in enormous numbers there can be no doubt. It is a striking fact, ascertained by Virchow, that connective-tissue, 234 MANUAL OF HISTOLOGY. Fig 224—Pus corpuscles in the interstices of tendinous tissue; from the tendo Achillis of the rabbit. which usually appears so quiescent and indifferent in the adult body, displays during pathological processes a new and mighty vigour of growth. . Simple inflammatory irritation alone gives rise to a rapid swelling-up of the cells contained in the interstices of the tissue. In the dull proto- plasm of these we may remark division of the nuclei also, in non-vascu- lar parts like the cornea, as well as in vascular structures (Strieker and Norris). We have already seen (p. 129) that pus corpuscles (lymphoid cells) may frequently accumulate in the passages and interstices of connective-tissue (fig. 224) in great quantities, owing to such irritation, arriv- ing there partly from the circulation. But others originate in the tissue itself; and it has been by some maintained now for many years, with the utmost certainty, that the parents of these are the connective-tissue corpuscles. But the mode of this origin requires nearer investigation than it has as yet received. It is possible that the membraneless connective- tissue cell may divide into these lymphoid ele- ments by simple or double nuclear segmenta- tion. Owing to its wide distribution throughout the body, connective-tissue plays the most important part in pathological neoplastic processes. Loss of substance in the organs of the middle germinal plate is replaced by it (cicatricial tissue) just as it may take the place physiologically of degenerated organs. Luxuriant growth of this structure causes an increase in quantity of the sustenta- cular substance of glands and other parts, as well as thickening of mem- branes, and so on. Numerous new formations, in the form of tumours, from the simple wart up to the supporting tissue of the most dangerous cancerous growths, consist of it. Tumours consisting of pure connective- tissue, Avith a more or less dense texture, have been given the name of fibromas. The starting-point of these is in most cases ordinary or physiological connective-tissue, with an undoubted participation of lymphoid cells. The appearance of such a pathological connective-tissue is very vari- able. Beside the most fully developed texture, such as only formed con- nective-tissue can show, we meet Avith structures of a softer species allied to the so-called formless kind. We encounter also appearances such as are presented by the young embryonic tissue. Thus, wherever a rapid development of the tissue is taking place, soft fusiform and stellate cells in close juxtaposition are observed, or there may be merely round and very primitive elements with scanty intermediate matter to be seen. It appears, also, that nucleated formative cells without a membrane may coalesce owing to their abundant protoplasma, forming more or less homo- geneous multi-nuclear masses. This must have been the origin of the many alleged exudations with spontaneous generation of nuclei spoken of in former days. We leave the rest to the hand-books of pathology, and pass on in the next section to the origin of the tissue. TISSUES OF THE BODY. 23o §139. The first indication of the formation of connective-tissue is the appearance at an early foetal period of delicate embryonic cells (fig. 44, p. 66), crowded together, without any membrane, and containing vesicular nuclei. These are held together by a small amount of an albuminous intercellular substance, so that connectiA'e-tissue and cartilage commence both of them with extremely similar primary forms. This first con- dition of rudimentary connective-tissue, however, is only very transient. The further transformations take place with equal rapidity, and are of different kinds in the various connec- tive-tissue structures. If these remain poor in blood, as, for instance, the tendons, the cells preserve their original crowded position, but become fusiform (fig. 225). If, on the other hand, they become vascular, as is the case with subcutaneous cellular tissue, an outpouring of a plasmatic fluid containing albumen and mucin takes place: the formative cells separate from one another, and assume frequently stellate figures (fig. 226). But even already all these cells ha\'e undergone metamorphosis. Their processes have broken up into a number of the most delicate fibrillae, which are at first straight, and contain abundant granules of protoplasm between them. Later on the latter withdraw more toAvards the middle of the cell, and the original cell- fig. 225.—Fusi- form cells from embryonic con- nective-tissue. Fig. 226.—Stellate cells from the same. Fig. 227.—Soft conneetive- t.'ssue from the neigh- bourhood of the tendo Achillis of a human em- bryo of two months old. Fig. 228.—From the tendo Achillis of a pig embryo 8" long. A, the fusiform cells and their fibrous intermediate matter in profile; B, transverse section (spirit of wine preparation). body diminishes to a corresponding degree in volume. The fibrillae then assume gradually a more and more wavy character, and are con- verted into an ordinary bundle of connective-tissue fibrillar (the interstitial molecules disappearing at the same time) (Breslauer and Boll), or into single fibrd (Kutznetzoff and Obersteiner). From personal observation we 236 MANUAL OF HISTOLOGY. are inclined to accept this as the correct view, although Rollett supposes the connective-tissue fibres to have their origin independently of the cell. The fasciculi, according to this, spring from the metamorphosis of the original cell-body, or, if we prefer an expression of M. Schultze1 s, are pro- duced by "the formative agency of the protoplasm." We refer the student to figs. 227, 228, 229, and 230, almost all of which apply to the development of solid connective-tissue masses poor in blood-vessels and intermediate fluid. Such appearances Avere known long ago to Schwann, who interpreted them quite correctly. Later on the connective-tissue fibrillae were sup- posed to be formed by a metamorphosis of the intercellular substance,—a theory for which at last even Koelliker declared himself. At the present day, when the absence of an envelope on the connective- tissue cells is looked upon as certain, and the intercellular substance is regarded as at least in many cases a metamorphosed external part of the cell-body, as in cartilage (p. 167), the relationship of the cell-body to the fibrillae appears again such as indicated by Schwann. From the length of mature connective-tissue bundles, it may be inferred that the fibrillae of adjacent cells unite in a longitudinal direction in their formation (Boll). We turn now to the inquiry, what is the further destiny of the so much impoverished formative cell of connective-tissue 1 It appears to vary in different ways. In some cases this cell persists, separates from its product the fasciculus, and is transformed into that frequently flattened, sometimes smooth-edged, Fig. 229.—a, Fusiform, apparently forma- tive cells of connec- tive-tissue fasciculi; b, cell-body and fibrillar substance still distinguishable. Fig. 230.—A fusiform cell from the tendon of an embryonic pig 8 inches long, a, a cell with protoplasm; 6, connective - tissue fibrillas (spirit of wine preparation). sometimes jagged element with which we have become acquainted through the investigations of Kuhne, Ranvier, Flemming, and Boll, as the cell°of mature connective-tissue (comp. § 129). Again, the nucleus remains behind with a small (fig. 230) or frequently almost imperceptible residue of protoplasm. This is the case in those connective-tissue structures Ave have already considered, in which appa- rently naked nuclei are met with in the fibrous mass (§ 132, for instance ) Thirdly, the nucleus seems, in some cases, to disappear 'early with its scanty remainder of protoplasm, by commencing fatty degeneration (Boll) TISSUES OF THE BODY. 237 so that we may only meet with fasciculi intermixed with elastic elements, but Avithout a trace of the original formative cell (comp. fig. 201-203). We must still leave it an open question, whether lymphoid cells which have Avandered out of the foetal blood-vessels may not be transformed into formative cells of connective-tissue. It seems, however, probable. The mode in which elastic fibres have their origin, though compara- tively easy to observe, has been long a subject of controversy. And although the manner of their separation from the interstitial substance remains up to the present completely unexplained, still there can be.no doubt that they originate independently of the connective-tissue cells. In § 136 Ave spoke of the ligamentum nuchae of the adult mammal as a mass abounding in elastic fibrous netAvorks, and in which no corpuscles are to be found. Now, it Avas from this tissue in question that Muller, and subsequently Henle and Reiehert, obtained proof of this. If *we examine the ligamentum nuchae of very small foetuses, Ave observe the same to consist of numerous spindle-shaped cells arranged longi- tudinally, and of an intermediate substance with- out any elastic elements. Later on (fig. 231, .4), we recognise exactly simdar fusiform cells, Avith considerable sized nuclei and short pointed ex- tremities (a). Between these there appears an indistinctly fibrous matter (b). Even here nothing is seen of the elastic elements until the Avhole has been treated with boiling potash (B), Avhen the cells are destroyed, and a net- Avork of extremely fine elastic fibres becomes visible. If we continue our research on older embryos, we find these fusiform cells becoming thinner and longer until they gradually disappear. In the new-born animal only traces of the latter are to be seen. The elastic networks increase in density in the same proportion, and their fibres in strength. The bundles of connective-tissue also become more apparent in the ligamentum nuchae (Koelliker). The above sketch of the development of con- nective-tissue will, no doubt, receive, through continued research, many additions, the more so as our acquaintance with the subject must be looked upon as being merely in its commencement. If we inquire into the mode of appearance of connective-tissue in the body, we find that it may be classed into a primary and secondary. The primary is from a metamorphosis of the cells of the middle germinal layer. The secondary, also from the same embryonic layer (never from the corneous and intestinal glandular leaf), takes place usually from other members of the connective-tissue group, most probably from lymphoid corpuscles. As an instance of secondary formation of connective-tissue, we may cite the process of the production of bone to be described in the following section. In pathological novogenesis, also, the formation of the tissue takes Fig. 231.—From the ligamen- tum nuchae of an embryonic pig 8 inches long. A. la- teral aspect; a, fusiform cells in fibrillated ground substance, 6; B, elastic fibres, c, rendered visible by boiling in potat.li. (Spirit of wine preparation.) 238 MANUAL OF HISTOLOGY. place in the same manner as has been described above for the normal structure. But that many subordinate peculiarities may make themselves evident here must be granted. Remarks.—We should be obliged to overstep the bounds of a work of this kind by a great deal did we enter more minutely, or in a manner which could be regarded to any extent as exhaustive, upon this still unsettled question as to the origin of connective-tissue. In the year 1839, its mode of origin was held by Schwann to be the following:—Cells, originally spheroidal, took on the fusiform figure, and, becoming further elongated, underwent a splitting up of their substance into fibrillae, com- mencing at their extremities, thus giving rise on the metamorphosis of the latter into the so-called bundles of connective-tissue. As to the destiny of the nuclei of these formative cells, it remained unexplained, and the development of elastic fibres from other cells was looked upon as probable. Henle, however, appeared soon after as propounder of a new theory of origin, in consequence of renewed investigation. According to his view, connective-tissue consists of an originally nucleated blastema, in which the nuclei are arranged Avith regularity, and the ground substance splits up into bands following their direction. By a fibrillar metamorphosis of the latter, the ordinary fasciculi are produced. At the same time, the nuclei are supposed to become elongated into fusiform bodies, which may subsequently unite, forming fine elastic fibres (Kernfasern). No personal investigations have been published by him as to the formation of the larger elastic filaments. In 1845, Reiehert brought out a very important work for the history of connective-substance. In this he taught that between the original cells of embryonic connective-tissue an intercellular matter gradually makes its appearance, the former coalescing with this to form a homogeneous mass, so that in that the nuclei are still recognisable ; we have arrived at about the same starting-point as that maintained by Henle. Later on, the nuclei were supposed by him to disappear in part, while the occurrence of fusiform cells was denied, and the objects which had been held to be such were declared to be (together with the fibrillar of connective-tissue) artificial products, as already mentioned. Elastic fibres were regarded as transformations of the ground substance. In the year 1851, however, there came a turning-point, through the works of Virchow and Bonders. These investigators demonstrated, with the scanty aids to research of the time, in the first place, the persistence of nucleated cells, and laid, Avith perfect justice, the chief stress on these elements of the tissue. They fell, however, into a dangerous error in regard to the origin of elastic fibres, in that they supposed the latter to take their origin from a change in these cells. According to both observers, the latter never take the form of connective-tissue bundles, but enter into the construction of stellate and fusiform corpuscles, which may unite to form elastic tubes and fibres. The latter, as a rule, have origin only from such cells (a point long defended by Koelliker): True connective-tissue is intercellular substance. This view, supported by Virchow and Bonders, was at once attacked by Henle in the most determined manner ; the stellate cells were declared to be the transverse sections of interstices between tlie bundles of Conn»erive-tissue, and the whole to be an optical illusion. Now, although Henle, Ave must confess, has in many respects gone too far, still he is entitled °to praise for having directed attention to errors in the theory just mentioned as that of Virchow and Bonders. On the other hand, this new theory, sometimes unchanged, and some- times with greater or less modification, was received (and further developed by observation of the normal as well as diseased tissues) by a number of new adherents of the two men just named. The formation of bundles of connective-tissue from cells, iti the sense in which Schwann spoke of it, has only been supported (among men of any note) by Koelliker, up to the year 1861, when he too gave it up ; all others have regarded the fasciculi and fibrillae as metamorphosed intercellular substance. Again, a new era was initiated by a paper by M. Schultze in Reiehert and Bu Bois- Reymond's Archiv. 1861, p. 13. In this he proclaimed the formative cell of connec- tive-tissue to be membraneless, like other youno- cells. 10. The Tissue of Bone. § HO. Bony or osseous tissue is a member of the group of connective- substances, by no means springing in the first instance and immediately from the cells of the middle germinal plate. It is rather formed TISSUES OF THE BODY. 239 secondarily from metamorphosed descendants of cartilage or connective- tissue cells, and may therefore be regarded as the most complex structure of this group. It consists of a netAvork of stellate ramifying spaces containing cells, and an abundant intermediate substance of homo- geneous nature. The latter is remarkable for its extreme hardness and solidity, and renders the whole the most resistent of all the more widely spread tissues. Its specific gravity in the compact substance of holloAV bones is T930; in the spongy, 1*243 (Krause and Fischer). As the name expresses, the occurrence of this tissue is in the human body normally confined to the bones, if Ave except a thin coating on the roots of the teeth. Its distribution, however, among the vertebrates, pre- sents considerable variety. As is well known, bones are divided by anatomists according to their form,— into the long or cylin- drical, the flat or tabular, the short or irregular. Again, in accordance with their texture,—into the compact (in Avhich the tissue has the appearance of a solid continuous mass), and the spongy or cancellated, in which the osseous substance, occur- ring in the form of bands and plates, encloses a sys- tem of cellular intercom- municating cavities. The cylindrical bones display a compact texture, except in their terminal portions or epiphyses, Avhilst those belonging to the short or irregular class are formed of spongy tissue, Avith the exception of their super- ficial layers. In tabular bones Ave encounter spongj' substance or dip- lde clothed externally by lamina? of a very hard tissue known as vitreous layers (Glastafeln). The great hardness of Fie 232 —Perpendicular section through a human phalanx. At a and b, two medullary canals with branches, c and d; e, the orifices of oanaliculi appearing as dots; /, osseous cells filled with air. osseous tissue does not admit of the usual method*? of examination being applied to it, and we are obliged either to have resource to plates which have been sawed out and ground thm, or Ave must extract from the tissue its solid mineral constituents, after which the decalcified remainder (bone-cartilage, as it has been inappropriately 240 MANUAL OF HISTOLOGY. named) or ossein permits of being cut up owing to its cartilaginous consistence. In vertically cut plates of compact substance from long bones (fig. 227) we may recognise the following points. The Avhole is traversed by a system of canals formed of longitudinal passages connected in a reticular man- ner with one another (a, b, c, d), and having an average diameter of 0*1128- 0*0149 mm., with extremes on both sides. These run more or less parallel Avith one another, separated by in- tervals of about 0*1128-0*2802 mm. At certain intervals also connecting tubes are seen passing between these at one time directly transverse, at another rather more obliquely. If the section include the whole thickness of the bone, some of these canals may be observed to open freely into the medullary cavity internally, as well as externally toAvards the periosteum, Avidening as they do so into funnel- shaped orifices. Towards the ends of the long bones, in the neighbourhood of their articular cartilages, certain bends in the course of the medullary canals may be observed. This system of passages is destined for the adm ission into the bone of the blood- vessels necessary for its nutrition. The passages themselves are known by the name of Haversian or medullary canals. Transverse sections, as fig. 233, have of course quite a different appearance. Here we see, at corresponding dis- tances, the severed ends of the longi- tudinal canals in the form of rounded apertures (c, c); or should the section have been made someAvhat obliquely, of more or less oval deficiencies of substance. Again, if the cut have fallen in the plane of one of the transverse intercommunications between two such canals, the latter appear as round holes connected by an open slit. Intermediate forms occur also as a matter of course. This beautiful regularity, however, presented by the central portion of a long bone, is more or less at an end in other than compact osseous tissue. In the external crust of tabular bones, the Haversian canals generally run in a direction parallel with the surface; in most cases also radiating from a central point. In the short bones also there is usually one preponderating direction in their course. In the bands and septa of spongy osseous tissue, this' system of medullary canals is far less strongly developed, the latter frequently opening into the cancellous spaces with funnel-shaped enlargements Fig. 233.—A portion of a human metacarpal bone in transverse section, a, external, 6, internal, surface with their respective gene- ral lamellaj; c, transverse sections of Haver- sian canals surrounded by their special lamella?: rf, intermediate lamellae; e, bone corpuscles with their ramifications. TISSUES OF THE BODY. 241 Several Haversian canals may often be seen also uniting with their enlarged ends to form a small medullary cavity, betAveen which and the larger kind many intermediate forms exist. Remarks.—Beside the German works on the subject, compare Tome's article, "Osseous Tissue," in the Cyclopedia of Anatomy and Physiology, as well as the excellent treatise of Tomes and Be Morgan in the Phil. Transact, for the year 1853, part i. p. 109. §141. The hard homogeneous osseous tissue between these Haversian canals has a laminated structure, explained by the mode of origin and formation of the mass in successive portions. These lamellce are united in the most intimate manner with one another, but may be separated in macerated bone which has been deprived of its mineral constituents. The systems of laminae, however, are of two classes. In one of these the leaves affect the Avhole thickness of the bone, in the otheT they are arranged round the individual Haversian canals. We may designate the first as general or fundamental, the others as special or Haversian lamellae. Nowhere can this be better seen than in a transverse section of the middle portion of a hollow bone, such as we have in fig. 233. The general lamellae are here distinguishable as a system of concentric layers traversing the Avhole thickness of the piece : commencing internally (b) around the central medullary canal of the bone, whose walls they form (medullary lamelke) ; then usually less distinct in the middle portion (d), with numerous interruptions (intermediate lamellae), and on the other hand appearing in the most distinct manner again externally towards the periosteum (d) (periosteal lamella?). Of course these stratifications belong to one and the same system of lamellae. The number and the thickness of the individual leaves is subject to variation. The latter amounts to 0*0077-0*0156 mm. and upAvards. The special lamellae surround the Haversian canals in varying number—from 6-18, with extremes in both directions (c). Their thickness is, on an average, 0*0065-0*0127 mm., and their arrangement is, as a rule, more or less concentric, the most internal of them constituting the walls of the Haversian canals. The latter are not unfrequently situated eccentrically in their systems of lamellae. Should this be the case to any great extent, the latter may be incomplete towards one side, and it occasionally happens also that the systems of two Haversian canals are enclosed again in secondary lamellae (Tomes and De Morgan). The strength of these systems further round the canals is very variable. Those of the latter, which have a medium calibre, usually possess the strongest. In the heavier cylindrical bones of the human skeleton, the Haversian canals usually lie so close together that their concentric lamellae almost entirely obscure the inter- mediated ones; not so, however, in the smaller bones of the metacarpus and fingers, where the distance between them remains greater, as is the case generally among other mammals. If we prepare a longitudinal section of the compact substance of a long bone, the extended network of the Haversian canals will be seen sur- rounded by lines running parallel with their contour, and at the same distance from one another as those concentric ones of the transverse section. Thus the lamellae appear to be a system of tubes of consider- able length, disposed one within the other, and placed, as a rule, per- 242 MANUAL OF HISTOLOGY. pendicularly, only that the horizontal passages of communication are enveloped by corresponding lamellae. The latter may be best seen, though seldom, in the horizontal canals occurring in transverse sections, cut through in their length. In other parts of the skeleton this beautiful regularity is less marked. Thus we see, even in the epiphyses of the cylindrical bones, that these systems of lamellae are much less developed, that the medullary canals are enclosed within an inconsiderable number of the latter, while the more internal general lamellae are entirely missing. In spongy osseous tissue the laminated texture is rather more apparent in thick bands antl plates, while it disappears more and more as the latter diminish in volume. In the outer layers of flat bones the general lamellae, as well as the Haver- sian canals with theirs, run parallel to the surface. The same may be remarked with both systems in the compact layer covering the short bones. The great energy of the formative process in young bone often effects a re-solution of already perfect tissue, commencing in one of the Haversian canal-systems (fig. 234, a). This produces irregularly-bounded cavities of varying size, with eroded edges, and lamellae appearing as though gnawed away at points. Tomes and De Morgan, Avho first directed attention to this, have given to these the name of "Haversian spaces." Fig. 234.—Transverse section of a human phalanx, a* Haversian ro«tm „f n„> „ a- ■• « a, two others which have undergone re-ansorp.ion in thTEKr lib)Thus civinerise*)'fa rersian spaces, which are filled anew with lamell*; c another such iv^™ ^vS ,? tion has taken place for the third time, with subsequent depositonlwho?i- ™h» V-6"8*80/1" and e, ordinary intermediate lamella. "^"eni aeposit ot new bonj matter; d, irregular, Such a cavity may be_ subsequently filled up by a new system of special lamellae, its characteristic outline nevertheless betraying its ori-in (b b) Indeed, as I myself saw some years ago, in a human phalanx, one" of these systems occupying an Haversian space may undergo re-absorption for the second time from the centre, with a tertiary formation of concentric lamelhe ™£ "wT (C)" HTrTn SpaCei°£ tMs kind are of no ™y rare occur- rence When present m large number, they may impart to the bone con- siderable irregularity of texture. §142. Osseous substance, which may be numbered among the double refract- ing tissues, as the polarisation microscope teaches, has a raC homogt TISSUES OF THE BODY. 243 neous, but by no means very transparent appearance : it is, on the con- trary, tolerably dull and opaque. If Ave employ very strong magnifying powers, we remark at times, Avith tolerable clearness, a finely-dotted ap- pearance in the mass. Owing to this, many histologists (Todd and Bow- man, Tomes and Koelliker) look upon the texture of the tissue as being granular, which is denied by others (Henle and Gerlach). It appears more than probable, however, that the transverse sections of the finest of the canaliculi, though they do not entirely produce this appearance, do play some part in it. In transverse sections, likeAvise, Ave may distinguish on every Haversian lamella, with more or less distinctness, an external and more deeply shaded, and an internal and much lighter part—a difference the significance of Avhich is doubtful. t Attention has been directed rather recently to a peculiar system of fibres in the ground-mass of osseous tissue, namely, to the perforating fibres of Sharpey (fig. 235), (Sharpey, H. Muller, Koelliker (2), Gegenbaur). They are to be found in human bone and that of other mammals, but more frequently still in that of amphibia and fishes, appearing Avith a certain irregularity and variableness. Those systems of lamellae which are formed by the periosteum, namely, the general laminae, as well as the more superficial of the Ha- versian system, are pierced by the fibres in question, sinking into them from the perios- teum " like the leaves of a book by a nail which has been driven through them." They are frequently enlarged at one Fig. 235.—Sharpey's fibres (*>) of a periosteal lamella, from P1,fl ,nfn „ funnA* "linno Vint the human tibia, a c, osseous cdl-cavities. enU lnl° a lunnei "liape, DUl may also be pointed or branched, Sec. In certain localities they enter into the construction of a network, some- times Avide and sometimes narrow, in its meshes. In the holloAV bones of amphibia and mammals (fig. 236) this system of fibres consists of longitu- dinal columns (b b), from which radiating systems of branches (c c) pass off, piercing the lamellae in the direction of the periosteum, as Avell as toAvards the Haversian canals. In the substance of these fibres, but especially in their nodal points, we may encounter osseous corpuscles. Sharpey's fibres are connected Avith the periosteum; they are the residue of connective-substance, i.e., of bundles of connective-tissue dating from the period of the formation of those lamellae. The cells contained in their cavities have the significance of connective-tissue corpuscles also (Gegenbaur). The chemical bearing also of these mostly calcified fibres agrees likewise with this vieAv. In keeping Avith their origin from the periosteum, they must be absent in the systems of leaves, filling up the Haversian spaces (fig. 234). The most important elements of osseous tissue, however, are the cells of the latter, imbedded in it in the greatest abundance, and situated in the enlarged and radiating nodal points of a highly-developed system of canaliculi traversing the hard osseous substance. With these, therefore, we must occupy ourselves before passing on to anything else. This svstem of canals, Avhose finer branches are called canaliculi (Kalk- 244 MANUAL OF HISTOLOGY. kanalchen), while the wider spots or nodal points bear the name of'lacuna (Knochenhdhlen), was formerly held to be the source of deposit of the bony earths—an erroneous view, which has perpetuated itself in one of the names just mentioned. . The lacume (fig. 237) appear in fresh moist bone as oval lenticular Fig. 236.—Transverse section of the metatarsus of an ox (after Gegenbaur). a, Haversian canals; b, transversely cut columns of Sharpey's system of fibres, whose branches, c, are partly in con- nection with osseous corpuscles. cavities, sometimes short and at others more or less elongated, lying with one broad surface towards an Haversian canal. They have a transparent Fig. 237.—Transverse section of a hnman bone, a 6, two divided Haversian canals, surrounded by special lamellae c d; either sfngle and entire cells or^parts of the same sink themselves into the newly-formed lamella (fig. 245, g,f fig. 246, e), where they may be recognised in every stage of growth up to the stellate form, on assuming which they are no^ unfrequently connected by means of their processes with cont "uons cell" sssrs*and poorer m ^^ >™ " ^n:snr=^^ the formation of a second Avith new cells and so on 'iL \ ^ becomes thicker and thicker, assuming ."i^^^^ Fig. 245.—Transverse section from the femur of a huma,i embryo of about eleven weeks old. a, a medullary sinus cut transversely, and b another longitudinally; c, osteoblasts ■ a, newly-formed osseous substance of a lightercolour- e that of greater age;/, lacunae with their cells; g, a cell" still united to an osteoblast. TISSUES OF THE BODY. 255 Fig. 246.—Osteoblasts from the parietal bone of a human embryo thirteen weeks old (after Gegenbaur). a. bony septa, with the cells of the lacunae; 6, layers of osteoblasts; c, the latter in transition to bone cor- puscles. quence of its deposition in successive portions. This is the beginning of the laminated formation of bony tissue. We are still in uncertainty as to the mode of formation of the canali- culi during these processes. The characteristic peculiarity of osseous substance soon makes its appearance now,—namely, its calcification; not in granules moreover, but by a more dif- fused deposit of bone earths, communicating to the whole to a certain extent a translucent appearance. The organic sub- stratum of these layers is pro- bably from the \-ery commence- ment collagenous matter. Naturally enough, the irregu- lar form of the medullary sinuses, and continuous re-solution of the still remaining portions of cartilage, give rise to very dif- ferent appearances in the osseous tissue first formed, as we may see in fig. 241, or more strongly marked still in fig. 242. A transverse section, also, through the middle portion of the femur, discloses the same irregular struc- ture, the bone consisting principally of longitudinal septa connected by means of transverse bridges (fig. 243). Here, then, Ave have a contrast to the regular texture of completed bone. Those points are of special in- terest, as explaining the former error of supposing a direct transi- tion of cartilage cells into bone corpuscles, Avhere the ruptured cavity of a cartilage cell has been made use of as a receptacle for the deposit of one or more bone cor- puscles Avith the accompanying ground-substance. Here one, two, or three of the latter elements may appear to be contained in the in- terior of a closed capsule, owing to the ease Avith Avhich the open- ing of the latter may be over- looked (tig. 242, h,f; fig. 241, e.) But sometimes almost all the septa of a preparation of osseous tissue have this same extraordinary appearance, so difficult of description, Avhich may be better understood by a glance at fig. 242 (to the left, beloAv). By the gradual liquifaction of the remaining portions of cartilaginous Fig. 947. —Section of the frontal protuberance o! tlie calf (after Gegenbaur). a, hyaline, and 6, calci- fied cartilage; c, bone corpuscles. 256 MANUAL OF HISTOLOGY. substance, and the consequent acquisition of new spaces for the growing bony tissue, which lays down additional layers of progressively increas- ing thickness, at the same time that the canaliculi are being more and more developed, the new osseous substance takes the place of the pre- existing cartilage very extensively. That a residue of the original calci- fied tissue may persist in the interior of fully-matured bone appears certain, although at present Ave knoAV nothing definite as to the extent to Avhich it may do so (Tomes and de Morgan, Miiller). That a rapid and extensive re-absorption takes place in the formed bone Avill be seen later on. But apart from this re-solution of calcified osteoid tissue on a large scale, there is besides another hidden process in osseous tissue, by which older portions of the latter are dissolved, and new masses laid down in their place. This is first of all borne witness to by the nature of the medullary cells in old spongy bone, as compared to those of the same parts in younger individuals. And that there is an incessant disappearance of material of the same kind at a late period has been seen Avhen discussing at § 141, fig. 234, the formation of the Haversian spaces, and their being re-lined subsequently by neAv lamella of bony sub- stance. A direct transformation, hoAvever, of cartilage into osseous tissue does likewise occur, though as a rare exception. In such cases we remark certain jagged cartilage lacume in the calcified tissue (fig. 247, b), which have arisen from a peculiar mode of thickening of layers on the internal surface of the capsules. Later on the granular calcification becomes diffuse (c), the jagged processes of adjacent cells unite to form passages; in short, bone corpuscles and canaliculi (c) are produced. In these the cells lie in tAvos or threes. The frontal protuberance of calves and tracheal rings of birds afford the best examples of transformations of this kind (Gegenbaur). In rachitic bone, also, as has long been known, isolated spots of this kind are to be found with the same transitions going on in them. In the antlers of deer undergoing ossification similar changes probably take place to a more marked extent. §148. There still remains for our consideration the formation of osseous tissue in parts of the body where cartilage is not previously laid down, to be again dissolved in order to make Avay for the former. Under this head we shall have to discuss, first, the origin of bone from the periosteum, and^ again the ossification of the so-called secondary bones. The first of these, a process very extensively met with, and in its beginnings frequently preceding the ossification which takes place in cartilage, is the source of the increase in thickness of bones. Holding still to the example of the cylindrical bones, we know by ex- perience that the latter increase with the growth of the body, not only in length, but also considerably in thickness. The increase in length we may here mention, is a continuation of the process treated of intdie foregoing section: it takes place, namely, at the expense of the epiphysis and articular cartilages, whose deeper portions become calcified and then dissolved to make room for the advance of osseous substance. Durino* this time the cartilage also grows upwards by division of its cells and accumulation of its ground substance. The increase in thickness takes place in the following way :-New layers of bone are formed under the clothing periosteum which envelope the mass within in a series of tubes. TISSUES OF THE BODY. 257 It is hardly necessary to add that each newly formed ring must be larger than the older one formed before it. And the groAving bone also becoming lengthened, each of these osseous tubes is likeAvise longer than the preceding. The importance of the periosteum in the formation of bone has been further proved by Oilier through a series of remarkable experiments. Detached portions of this membrane, Avhether still in connection Avith the remainder of the structure or completely separated from it, have the poAver of generating again a complete bone; and not only in this case, but even when transplanted to other parts of the body, or from one animal to a second of the same species. But the deeper layer of the periosteum must be carefully preserved in doing this,—a precaution which Ave will presently understand. If Ave noAv turn to the histology of the process (fig. 248), Ave must first recall to mind the structure of the fibrous periosteum (p. 226), Avhich is more vascular at an early period than later on. The latter consists internally (Blasthne sous-periostale of Oilier) of a mass of young connective-tissue, not fibrous, but formed of fusiform and stellate cells (b). Under this appears the stratum of Gegen- baur's osteoblasts (c), which generate the osseous tissue here, as in the interior of cal- cified cartilage, and in the same manner. Both pro- cesses, the intracartilaginous as well as the periosteal, are therefore identical. The newly-formed bone (fig. 248, c) is irregular, and jagged towards the still soft external layers, and is traversed in the interior by sinuses, giving it a spongy texture. These are filled Avith medullary cells, and covering the latter Avith osteoblasts, and become eventually Haversian canals. Thus the osteoblasts, as in the intracartilaginous formation of bone, give rise also to the production of the special lamelke of the Haversian passages (a). Bundles of connec tive-tissue which penetrate this new layer of bone ossify immediately, and are known later as Sharpey's fibres (§ 142). During all this, however, the secondary formation of the great medul lary cavity introduces new changes into the young osseous tissue. W hen we remember the large dimensions of the former, it is easy to conceive the great quantity of the latter which must undergo re-solution in its produc- tion. Fig 248.—Formation of secondary bone. Longitudinal section of the femur of a well-grown fcetal sheep, u, the internal layer of the periosteum, consisting of con- nective-tissue; b, younger stratum, or Ollier's layer of the periosteum; c, layer of osteoblasts; d, newly-formed osseous tissue; «, lacunae and cells. 258 MANUAL OF HISTOLOGY. If Ave remember, also, that the cavity in question of a fully groivn bone occupies more space than is taken up by the entire bone at an earlier period of life, Ave see that the Avhole of the primitive osseous tissue must have fallen a prey again to absorption, and the mature bone consist of osseous substance formed only from the periosteum. The .ayers supplied by the latter are the general lamellae, as is easy of com- prehension, and as may be seen in every section (fig. 233). Of course, from Avhat has just been stated, it will be remarked that the oldest of them that are present become eventually medullary lamellae, bounding the great medullary cavity. In regard to the details of this process of re-solution, to Avhich Ave have been obliged to allude so frequently, but little Avas knoAvn until very latety. From Koelliker's very extensive investigations, it Avould appear that modified multinuclear cells spring from GegenbauiJs osteoblasts, attaining considerable dimensions in some cases : these are closely applied to the undulating eroded borders of the " lacunae of Howship" of the dissolving bony tissue. These multinuclear ••giant cells" (discovered, to be sure, years ago) have been named "ostoklast" by Koelliker, Avho ascribes to them a power of dissolving the bone. I have not the faintest belief in their possessing this latter property. It is improbable that, at the same time that this takes place, the bone- corpuscles formerly enclosed in ground-substance are set free, and, becom- ing medullary cells by retrograde metamorphosis, provide for the necessary increase in the bulk of the marrow. In short and flat bones, on the other hand, a certain amount of the original bony tissue, sometimes greater, sometimes less, remains,—of that, namely, Avhich Avas formed at the expense of the cartilage. Remarks.—The investigations of L. Oilier are to be found in the Journ. de la vhysiologie, Tome ii. p. 1, 170, 468, and T. iii. p. 88, as well as in the Gazette midi- calc, 1S59, Nr. 37, and 1860, Nr. 12. A resume of these Avorks, with new experi- ments, appears in a new two-volume work of the same author, Traiti experimental ct clinique dc la regtniration des os ct de la production artificicllc du tissue osseux. Paris, 1867. § 149. We now come to the origin of secondary bones, or, better expressed, of those not previously moulded in cartilage. To these belong as is usually received, the fiat cranial bones, Avith the exception of the' under part of the occipital, Avhich is modelled first in cartilage; further, the upper and loAver jaw, the nasal, lachrymal, and palate bones, the vomer, zygoma, and, finally, the inner leaf of the Avings of the sphenoid and Cornua sphenoidalia (Koelliker). These spring up outside of the primor- dial skull from circumscribed spots, which spread out subsequently gaining rapidly in superficial extent. Here we first meet with a (true) osseous nucleus, which grows out in all directions, forming a network of bony bands and needles (Kalkbdlkchen and Kalknadeln), which are lost in the adjacent soft tissue. It is easy to recognise here, also, the simi- larity of the osteogenetic process to that in other parts of the system and to see that these bony bands are covered by a layer of osteoblasts (fig. 246). Much difference of opinion still prevails as to the nature of this ordinal tissue, as also of that of the corresponding subperiosteal stratum ° one party regarding it as an undeveloped connective-tissue substance and not TISSUES OF THE BODY. 259 cartilage (Koelliker), and another as a kind of fibro-cartdage (Reiehert). The latter view is decidedly incorrect: we have before us most unmis takably a young and undeveloped connective-tissue, Avith fusiform and stellate cells. The diffuse calcification now advances superficially, as has just been remarked, accompanied by a border of osteogenic tissue, so that the full size and ultimate form of such a secondary bone is only attained gradually, in contradistinction to the cartilaginous preformations of the first kind. In order noAv that the bone may increase in thickness, a deposit of osseous substance takes place from the periosteum on both surfaces, and so the compact external layers are formed, which present at first all the porous characters of neAvly-formed periosteal bony tissue. The deposit of osteogenic matter from the medullary spaces resembles the process as it occurs in bones previously modelled in curtilage. These observations tend to show Avhat energy exists in the groAvth of osseous tissue, an energy in Avhich may be manifested afresh in fully developed bone, especially under abnormal conditions. But though these processes, as Ave see them in the development of cylindrical bones, are so far clear, we must not think that a solution internally and a deposit externally alone takes place : there is some- thing more, namely, an interstitial and expansive groAvth ("a groAVth by intussusception"), such as is to be observed in almost all tissues (R. Volkmann). But highly developed connective-tissue may also, under certain circum- stances, be transformed directly into bony substance. The flat cranial bones of embryonic birds (fig. 249) present to us most unmistakably, according to Gegenbaur, a process of this kind. Here a network of connective-tissue bundles is seen (c), in part still soft and fibrillated and in part granularly calcified (d). Later on these bands of hardened tissue become broader, are noAv diffusely calcified, Avhile the cells enclosed in them remind one of bone-corpuscles. A layer of osteoblasts (b, e) is also demonstrable here, Avhich deposits that stratum of bone clothing the connective-tissue frame- Avork. That we have to do here Avith an occurrence which, taken gene- rally, has been already discussed in referring to the formation of Sharpey's fibres, is quite apparent. The conA'ersion of tendons into osseous tissue is Avell knoAvn to take place largely as a physiological occurrence in mature birds. Here Ave encounter, at first, a simple calcification of the connective-tissue, so that, on depriving the part of its bony earth, the tendinous texture is again presented to us unchanged. Later on, however, true osseous substance makes its appearance, with a small number of lacunae, lamellae, and Haversian canals. It Avas formerly supposed that here a direct transfor- mation took place from tendinous into osseous tissue (Licberkuhn), but this is an error. There appear, rather, in the calcified tendon, spaces containing vessels Avhich correspond to the medullary sinuses of cartilage, and are filled Avith a soft mass. From these cavities the deposit of a solid substance takes place, which becomes calcified at once, " resembling true bone more or less" (H. Muller). Remnants of calcified connective-tissue are left, hoAvever, in these ossified tendons. Regeneration of osseous tissue occurs pathologically, with great fre- quency, on the fracture of various bones,—for the repair of breaches of continuity and replacement of lost substance, Avhether it have been thrown off by a pathological process or removed by surgical instruments; 260 MANUAL OF HISTOLOGY. hypertrophies, exostosis, mther, in uninjured bones a luxuriant growth may occur, in the form of and osseous tumours. In most ot these cases the production of the neAv tissue takes place from the periosteum in the manner described. "With- out this, however, Ave may be satisfied of the great importance of the membrane in the produc- tion of bone from Oilier's experi- ments (p. 257). But Avhile the me- dullary tissue remains inactive in the normal formation of bone, as Avas ascertained by the inves- tigator just mentioned, it may, under abnormal conditions, be- come transformed into a more or less solid connective-tissue on its exterior—into a species of endosteum, and generate bone- like matter. The latter is rarely developed in soft parts remote from bone. The formation of true osseous tissue independent of bone is very circumscribed. It takes place, however, far on in life in cartilage, and at its ex- pense, when the processes of foetal ossification are repeated; likeAvise in parts formed of con- nective-tissue, Avhen a groAvth similar to that from periosteal osteogenic substance is the start- ing point. Masses of bone formed pathologically have frequently a porous character at first, resembling the normal tissue, but may also be com- pact, and.endoAved with a high degree of solidity. The occurrence of re-solution of normal osseous tissue is by no means rare in disease. It takes place Avith previous decalcification, in the same Avay as physiological absorption in growing bone. Remarks.—From the fact that bones not previously modelled in cartilage are in many cases developed before those others become ossified which are thus pre-formed, we may perceive that the designation "secondary" has not been very happily applied to them. An attempt has been made, therefore, to replace in by the names " teguiuentary or overlaying bone" (Deck-or Belegeknochen). The whole thing has lost considerably in histological worth, however, according to the latest observations in osteogenesis. 11. Dentine. §150. Before entering upon the description of dentine (1), it will be necessary first to devote a few words to the consideration of the teeth, the neater part of which it forms. A tooth may be divided into three distinct parts,—into the crown, Avhich lies exposed; the neck, enclosed in the gum; and the root, buried Fig. 249.—From the edge of the frontal bone of a chick undergoing ossification (from Gegenbaur). a, network of osseous bands; d, granularly calcified, and c, soft connective-tissue; 6, e, osteoblasts. TISSUES OF THE BODY. 261 crown, in the alveolus. It is hollow internally, traversed by a canal Avhich commencing above in the crown, terminates below at the point of the root by a free opening. In the incisor and canine teeth this cavity is single, and is divided in the others according to the number of their roots. It is filled Avith a peculiar connective-tissue, very vascular, and laro-ely supplied Avith nerves, Avhich is called the pulp. The nutrition of the whole organ takes place from this as from the Haversian canals of bone. From a histological point of view the tooth may be regarded as made up of three kinds of tissue (fig. 250),—of a coating on the root, called the cement, i.e., a bony substance; then of a layer covering the knoAvn as the enamel (see next section); and finally, of a mass situated internally, the proper tissue of the tooth surrounding the cavity just mentioned. This has received the names of the " ivoi-y," " dentine." The latter possesses a hardness exceeding that of bone, and must be looked upon as a species of the latter without bone-corpuscles, and with a more regular course in its canaliculi. It appears white, in thin sections, with a satiny lustre frequently, as long as the system of canals is filled with air and is not occupied by a fluid. These passages or dental canaliculi appear, in dried sections containing air, as extremely numerous and fine dark tubes of from 0*0011-0*0023 mm. and upAvards. They maintain a tolerably parallel course, side by side, perpendicular to the surface of the cavity of the tooth. This is consequently vertical in the middle of the crown (fig. 250), oblique at the sides of the latter, becoming horizontal below towards the root (2). In transverse section the middle and under portions of a tooth display a radiating arrange- ment of the canaliculi. If the latter become filled Avith fluid, they blend into the ground-substance and are rendered partly or altogether invisible, reminding us of Avhat takes place in bone under similar circumstances. They correspond farther Avith the canaliculi of special lining layer, Avhich is, however, thicker than macerated dentine this layer appears on sections in the form of tubes projecting beyond the surface. The latter may be easily isolated by the softening action of acids, as well as boiling of the tooth-cartilage or treatment with alkalies, on Avhich they are pre- sented to us as intercommunicating structures (Koelliker, Hoppe, Neumann, Frey, Waldeyer). In suitable sections of dentine we may likeAvise see the canals transversely opened (fig. 251). If we now examine into the more minute arrangement of the canaliculi in thin leaves of dentine containing air, we find their number to be greater in that portion of tissue surrounding the central cavity, and in the croAvn, than in the root. We remark also in the Avhole course of one of these tuber*, Fig. 250.—A human in- cisor, with the cavity in the axis surrounded by dentine, which lat- ter is covered above by enamel, below by ce- ment. bone in having a the latter. In Fig. 251. — Softened dentine, with trans- verscly cut canali- culi. 262 MANUAL OF HISTOLOGY. from Avithin outwards, usually three, or sometimes only two, undulating curves (known as the lines of Schreger), and Avithin these again a number of very small jagged or spiral bends, of which about two hundred may be seen iu the length of a line (Retzius). Like the canaliculi of bone, those of dentine (fig. 252, e) are observed to divide over and over again, and to com- municate through their branches; though in other respects they differ, owing to their more regular course. In the internal portions of the dental tissue a number of divisions take place at acute angles, and in rapid succession, Avith decrease in the size of the branches. This becomes more rare externally, gain- ing again in frequency in the most super- ficial portions. Thus from one canal a whole system may be produced. We encounter further, in many cases, intercommunications between adjacent canaliculi by means of oblique branches (c). This may lead eventually to the formation of a regular network iu the external portion of the tissue (fig. 253). Here some of the canaliculi join in loops (fig. 252, c), whilst others sink down into the cavities of a granular layer situated at that part (b), and a third set advances beyond the limits of the den- tine into the cement (fig. 252, a), or perhaps (I) into the enamel (fig. 253, c). We will meet with these again. Internally, this system of canals terminates by free openings in tlie cavity of the tooth. The ground-substance of dentine, finally, is a homogeneous substance Avhich may be split into bands artificially after maceration. The direction in Avhich this cleavage takes place is determined by the course of the canals. In addition to these elementary and essential features of the tissue in question may be added some of minor significance. For instance, a certain system of irregular cavities, of extremely variable size, named by Czermak " interglobular spaces" (fig. 152, 6), exists normally in this tissue, the interstices between the projections of a number of more or less spheroidal masses aggregated in the ground-substance, known as " dentine globules." The cavities in question are found, very numerous and small, principally under the cement covering or crusta petrosa, ofthe root. They here enter into the construction of the so-called granular layer of Tomes, and may be confounded with lacunae, more especially as they receive into them the terminations of canaliculi. These interstices, however, contain no air during life but a soft organic mass. lrig. 252.—External portion of human den- tine d, with coating of cement a; at 6, the granular or Tomes' layer of the first of these, with interglobular spaces; c and e, canaliculi 1'ig. 253.—External por- tion of dentine, d, from the crown of a tooth, with its layer of enamel *>. a, enamel cuticle; c, interstices filled with air. TISSUES OF THE BODY. 2G3 Larger globules of dentine may make their appearance internally on tho boundary wall of the cen- tral cavity of the tooth, communicating to it here, as has been very well said, a "stalactitic" appearance. In the croAvn Ave may fre- quently recognise concen- tric tracings running more or less parallel to the sur- face, probably pointing to a kind of lamination Avhich may hereafter find its explanation in histo- genesis. These are the so-called " contour-lines " of Owen. We have already re- marked that dentine may be regarded as a species of bone. Comparative his- tology also teaches us that the osseous tissue of many bony fishes supplies inter- mediate formsbetweenbone and dentine, and that in no inconsiderable number of these the latter appears in the place of osseous tissue (Koelliker) (3). Remarks.—1. Beside the German works of Henle, Gcr- lach, and Koelliker, comp. Todd and Bowman (Vol. 2). Fur- ther, R. Given—Odontography, etc. Vol. 1 ; Lond. 1840-45. J. Tomes—A Course of Lectures on Benlal Physiology and Sur- gery. Lond. 1848; and Philos. Transact, for the year 1856, p. 515. Beale. The struc- ture of the simple tissues. 2. Fig. 254.—Premolar tooth of the cat (after Waldeyer). 1, enamel with cross and parallel streaks; 2, dentine with so-called lines of Schreger; 3, cement; 4, periosteum of alveolus; 5, bony tissue of the lower jaw. In the many-pointed crowns of tho back teeth the direction of the canaliculi is the same as if every knob were the crown of a simple tooth. BetAveen the many roots on the so-called alveolar surface, as Purkinje has very happily named this part, the perpendicular course of the middle portion of the croAvn is again re-established. 3. Subsequently to Gucckett's having directed attention to this in certain fishes (Catalogue of Surgeons of England, Vol. 2), the above-mentioned German investigator proved the frequent and extensive occurrence of this interesting relation. §151. The pulpa dentis is the unossified remainder of the papilla existing in the embryonic tooth (see below). It is a kind of undeveloped soft con- nective-tissue, possibly belonging to the mucous or gelatinous species, containing numerous cellular elements of elongated or round form. The intermediate substance, Avhich is not rendered clear by acetic acid, is 18 264 MANUAL OF HISTOLOGY. indistinctly fibrous, and devoid of elastic elements. The pulp is further rich in nerves and very vascular, almost presenting in transverse section the appearance of a cavernous tissue. The small arterial stem which pene- trates into its substance splits up into several branches, which advance through the latter, forming in the croAvn of the tooth numerous capillary loops, through Avhich transitions to veins having a similar course back again takes place. The nutrition of the tooth is presided over by these vessels. The nerves will be referred to in a subsequent section. To them is due the great sensitiveness of the tooth, which, as is well known, may increase to intense painfulness at times. The external surface of the pulp is covered by a laminated stratum of narrow cylindrical cells, 0*0452-0*0902 mm. in depth, resembling epithelium. These elements, 0*020-0*030 mm. in length, contain an elongated nucleus. They are connected in the first place Avith one another by means of their ramifications, and in the next Avith the deeper-lying cellular ele- ments : finally, they send off soft delicate processes, single or multiple. externally. The "dentine cells," or, as they have been more recently and better named, the " odontoblasts" (Waldeyer) (fig. 255, b), have been long knoAvn; but attention has only been directed gradually to their relations to the dental tissue. It used to be thought that the system of canaliculi Avas nothing but a series of canals possessing no formed con- tents, and only filled Avith a nutritive fluid (Lessing). Indeed, dentine appeared to pre- sent one of the most beautiful examples of a system of vessels for plasma in the Avhole group of connective-substances. But Tomes' discoveries, confirmed by the observations of Beale, Koelliker, Neumann, Frey, Waldeyer, Hertz, and Boll, showed the 'tJel^Zu^eT p£££ erroneousness of this older view. a portion of the canaliculi at a, We may easily convince ourselves, namelv and projecting at c beyond the .1 , .1 , , f, , , ' ■' fragment of dentine. (After ttlat ttle odontoblasts protrude those of their ■5ea'£° processes already mentioned as directed out- wards into the so-called canaliculi of the tooth (fig. 255, a), probably traversing the latter Avith their ramifications in their whole length; at least, they may be still seen in the crown of the adult tooth. It would appear also as though these fibres of Tomes, or " dental fibres," filled up the whole lumen of the passages. It has been supposed that the structures resembling °canaliculi isolated by means of maceration, are nothing but these ramifications of the den- tine ceUs. This, however, is not correct; for even after processes which must have destroyed all the softer parts of the tooth, after the most active decomposition, canaliculi endowed with a special wall may be laid bare (Neumann). This wall can just as little be looked upon as the calcified membrane 01 dentine eel s and their processes as in the corresponding elements of bone. It is here also, as in bone, a modified bounding layer of the ground-substance so that Ave are correct in speaking of "dental sheaths" (Neumann, Waldeyer, Boll). Tomes' view of^the matter is of great interest: he refers the -real sensitiveness of the dentine to the soft fibres of these cells. We shall TISSUES OF THE BODY. 265 have to discuss this point at greater length in a future section, Avhen con- sidering the termination of the nerves of the pulp. In passing, it wdi be convenient to touch here on the nature of the cement, or crusta petrosa, of the teeth. This commences at the termination of the enamel as a thin layer clothing the root (fi>s. 250 and 254), increasing in thickness below until it attains its greatest thick- ness at the point of the latter. It is, hoAvever, nothing but simple osseous tissue (fig. 252, a), and, like this tissue, generally greatly inferior in hardness to dentine and still more so to enamel. It is not always sharply defined against the ivory of the tooth. Its ground- substance is sometimes homogeneous and sometimes streaked : Avhen very thick it may also appear faintly laminated, but it rarely comes to the formation of Haversian canals. ~No bone-cells at all are found in the cement around the neck of the tooth, and they only become numerous towards the point of the root. Their size and shape, and the number of their ramifications, which is often considerable, are more liable to varia- tion than those of ordinary bony tissue. Some of these ramifications are united Avith the canaliculi of the tooth which have penetrated as far as the cement; others form anastomoses Avith adjacent cells (fig. 252, in the middle of a). These lacunae must not be confounded Avith clefts Avhich are frequently to be met Avith in the cement of old teeth in the form of irregular, branch- ing interstices. § 152. Dentine, Avhose specific gravity is 2*080 according to C. Krause, con- tains, notwithstanding its hardness, several per cent, of Avater: some analyses give 10 per cent. It consists, like bone, of a glutin-yielding substratum, rendered hard by a considerable excess of calcium and also magnesium salts. The organic substratum, determining the form of the structure, is collagenic matter Avithout any admixture of chondrin. An interesting observation has been made in regard to the Avails of the canaliculi, namely, that though they may be isolated by means of the stronger acids and alkalies, they remain for a time undissolved in a Papin's digester, in Avhich the ground-substance is transformed into glutin (Hoppe), shoAving that these canals are not formed of glutin-yielding matters. We have thus a similar condition of things as in the lacunae of bone and their ramifications. The dentine globules also are not convertible into glutin, and their substance offers even a more determined resistance to the action of acids than the other portions of the tissue. The bony earths of dental tissue consist of a considerable proportion of phosphate of calcium, Avith a smaller quantity of carbonate, and also— taking a more subordinate place—fluoride of calcium and phosphate of magnesium. The carbonate of calcium appears to be subject here to more A'ariation in amount than in bone. Fluoride of calcium Avas originally determined by Berzelius, and Bibra made the interesting discovery that the dentine of many mammals is comparatively very rich in phosphate of magnesium. Beside these, many other salts and mineral constituents are met with in the teeth, and also a small proportion of fat. Tho bony earths, taken quantitatively, amount in human dentine from 266 MANUAL OF HISTOLOGY. 27*61 20*42 0*40 0*58 66*72 67*54 3-36 7*97 108 2*49 0*83 1*00 71 to 78 per cent., while the collagenic substratum of the tissue (the so- called tooth cartilage) ranges about from 20 to 29 per cent. The folloAving two analyses of Bibra may be taken as an example. They refer to the dried dentine of human molar teeth. The first of these was from an adult male ; the latter from a woman twenty-five years of age. 1. 2. Organic collagenic substratum, Fat,....... Phosph. and fluoride of calcium. Garb, of calcium, ..... Phosph. of magnesium, .... Other salts, ...... As to tlie softer crusta petrosa, any distinction from dentine is doubt- ful. The investigations Avhich have taken place up to the present show somewhat more organic substratum yielding glutin. Its nature is other- wise similar to that of dentine. Bibra obtained from that of the human teeth, 29*42 (inclusive of some fat) of organic substance, and 70*58 of mineral constituents. §153. The development of the teeth (1), as productions of mucous membrane, is, even in its coarser outlines, a most difficult chapter in embryology. From the fourth month on of intra-uterine life, we remark in the human embryo preparation for the formation of the future milk-teeth. This takes place on the edges of the jaAvs, by the formation of closed follicles, from the floor of Avhich a papilla pro- jects into the cavity, destined to produce the dentine of the struc- ture, and, moreover, in the first place, that of the croAvn, Avhile the remainder enters into the formation of the pulp. These papillary structures, which re- semble in form the croAvn of the future tooth, are called the " ' tooth' or ' dental' germs." In fig. 256 Ave have a sketch of one of these follicles from a tolerably mature embryo, with its but ill-defined Avail of con- nective-tissue (a) and dental germ (/) containing numerous capillaries (g). The latter is covered by a peculiar structure, in the form of a cap, hanging down over its sides (b). This has been named he « enamel-organ," on account of its presiding over the produc- tion of the enamel, as we shall see presently. Its concave inferior surface is lined by a layer of narrow cylindrical cells (cl) covering the dental Fig. 25G.—Dental sac of a human embryo at an ad vanced stage of development, partly diagrammatic. a, wall of the latter, formed of connective-tissue, and with its outer stratum a1, and inner a2; b, enamel organ with its papillary and parietal layers of cells c ■ d, the enamel membrane and enamel prisms; e, dentine cells; /, d.-ntal germ, and capillaries' g; i. transition of the connective-tissue of the wall of the follicle into the tissue of the dental germ. TISSUES OF THE BODY. 2G7 germ, while its convex external aspect is covered by a similar coatin" of smaller cells (c). But though all is so far tolerably clear, Ave are now met by the difficult question, so variously answered at different times, as to how these several structures take their origin. Iiecent investigations, and the researches of Tiersch and Koelliker, supported at a later date by those of Waldeyer (with Avhich my own subse- quent observations correspond), seem to point to the following conclusions The parts which are contained in the dental sac are of various origin. The dental germ corresponds to a papilla of the mucous membrane, which becomes enclosed in the parietal portion of the fol- licle as with a sheath of the latter. Both these struc- tures have their origin from the proper tissue of the mucous membrane of the foetal jaw. The enamel organ, on the other hand, is a produc- tion, by reduplication, of the mucous epithelium, Avhich covers^ the dental germ, just as^i papilla of the mucous membrane is covered by cuticular tissue. But the mass Avhich has grown down into the gum has (in the phase in Avhich we see it in fig. 256) be- come completely separated, by the closing iu above, from its original source of origin. In order really to under- stand these relations, Ave must look back to a much earlier period of foetal ex- istence. Originally, before any trace of either dental germ or tooth sac is to be seen, the edges of the jaAvs, Avhich are marked with a slight groove knoAvn as the " dental groove," are covered by a thick ridge of epithelium, just over the spots Avhere tho future structures are to be formed. This latter has been named the " dental ridge" (2) by Koelliker (see fig. 257, 1 a, 2 a). The epithelium soon after commences to groAV doAvn from the dental groove into the substance of the mucous membrane, in the form of a leaf-shaped process, Avhich becomes curved downwards and iiiAvards, appearing sickle-shaped, in vertical transverse sections. To this the Fig. 257.—Developmentof the teethfrom Thiersch's preparations of embryonic pigs (vertical transverse sections ofthe upper jaw). 1, 2. From a small embryo: the right and left halves of the maxilla, a, dental ridge; 6, younger layer of epithelium; f, the deepest; d, enamel germ ; -, enamel organ ; /, dental germ; g, inner, and h. outer layer of the growing tooth sac. ;'. From an older embryo: rf, the style of the enamel organ ; i, blood-vessel severed; k, bony substance. The remaining letters as in 1 and 2. 268 MANUAL OF HISTOLOGY. name of " enamel germ" has been given (1 d). Its walls are formed of narrow cells arranged perpendicularly, and its interior is taken up by small round cells. Later on may be seen how various parts of this enamel germ (3) increase in breadth at their deepest half, at those spots where the development of the several dental papiUae is to take place, thus preparing the way for the formation of the individual enamel organs (2 d). It is the small round cells of the interior just mentioned which principally occasion this enlarge- ment, in that they gradually become transformed into the already Avell- known non-vascular gelatinous tissue (fig. 181) with stellate elements (2 e). After this the formation of the dental germ or tooth papdla (2/) takes place. This grows upwards against the under surface of the enamel organ belonging to it, and soon transforms the shape of the latter into that of a thick cap covering it over. The parietes of the follicle are now laid down from the adjacent tissue of the mucous membrane, but gradually and but ill-defined, and soon we may recognise an external and more closely interwoven stratum (2 h), and a thick internal layer of softer and looser texture (2 g). In fig. 257 (3) Ave have represented the stage of de\*elopment in question. At / is seen the dental germ projecting upAvards, beneath Avhich the lumen of a considerable vessel appears Avhich has been cut across (i), and the commencing bony portion of the upper jaw-bone (k). This germ passes continuously into the substance of the still unfinished Avails of the tooth follicle, Avhose external layer is to be An at h, and internal at g. But Ave recognise also, at the same time, that the style (d) of the enamel organ (e) has become strongly narroAved, owing to the growth upwards of the walls of the sac,—a process which is destined to effect a separation of the enamel organ from the mouth. But before this the formation of an organ of the future takes place from the style, namely, of the secondary enamel germ. This plays the same part in the rudiments ofthe permanent teeth as its predecessor did in the formation of the milk-teeth (Koelliker). A leaf of epithelium is seen to spring from this style, and to sink down into the tissue of the mucous membrane in a manner similar to that described as occurring in the formation of the first enamel organ. This leaf lies beside the latter in a central position. From this it would appear that the permanent teeth have for their formation a new dental germ, but the old enamel organ (4). When the further progress of this striking and interesting series of changes leads to the obliteration of the stalk-like connecting bands of epithelium betAveen the summit of the enamel organ and the epithelium of the jaAv, we arrive at the phase of deArelopment presented to us in fig. 256 : the parietal portions of the tooth sac have closed over the enamel organ, covering it in. Remarks.—1. Literature is very rich in essays on the development of the teeth. Compare (beside the older and more recent German writings) Goodsir, in the Edin- burgh Med. and Surg. Journ., 1838, No. xxxi. 1 ; Huxley, in the Quart. Journ. of Microsc. Science, vol. iii. p. 149, vol. x. p. 127, and vol. xix. p. 166 ; Magitot, Etudes sur le de'veloppement et la structure des dents humains, Paris, 1856 ; and also Comptes rendus, 1860, p. 424 ; Guillot in the Annul, des scienc. nat., 2 SSrie, Tome ix. p. 227; Jolly in the same, 3 Se'rie, Tome ii. p. 151 ; Robin ct Magitot in the Journ. de la physiologic, Tome iii. p. 1, 300, 663, and Tome iv. p. 60 ; as also in the Gaz. mid. de Paris, 1860-61, in many places. 2. For a long time Goodsir's TISSUES OF THE BODY. 269 description was held to be correct. According to him, the first item in the develop- ment is the formation of a groove in the edges of the jaws, taking place in the human embryo during the sixth Aveek. In this the twenty-teeth germs of first dentition take their rise. He supposed hollows to be formed around these by the subsequent develop- ment of septa between the several dental germs, and that these underwent later on a closure above. This theory of Goodsir was attacked most vigorously, at a later date, in the works of French histologists,—Guillot, Magitot, and Robin. According to the latttr, the tooth sacs, dental germs, and remaining parts, are developed, in the first instance, within the sub-mucous connective-tissue, quite independent of epithelium and mucosa. 3. Husky was the first to declare the whole enamel organ to be of epithelial origin. 4. In the fifth month of intra-uterine life there may already be seen new follicles, situated above the germs of the milk-teeth in an oblique position. They become, however, more vertical later on, and lie behind and beneath the milk- teeth. Their ossification is spread OA'er the earlier years of infancy. Since the histo- genic occurrences in both cases are similar, it will suffice if we confine ourselves in the text to the consideration of the milk-teeth. §154. The connective-tissue envelope of the tooth sac (fig. 258, a) consists (as Ave have already seen in the previous section), at an early period, of two layers, an external (a1) and an internal (a2). The first of these pre- sents a great denseness in its fibrous texture ; the latter, rich in cellular elements, preserves a softer and more gelatinous character. The inner surface of the dental sac assumes a more or less homogeneous aspect, and to such an extent sometimes that a hyaline terminal layer has been Bpoken of. The occurrence of villous projections of this inner layer, which are directed towards the surface of the enamel organ, is of great interest. They appear to be equivalent to the ordinary vascular papillae of a mucous membrane (1). A complex vas- cular netAvork, Avhich receives its blood from the vessels of the jaws and gums, traverses the Avhole parietal portion of the dental sac, and may be seen forming loops in the projections just mentioned. The enamel organ presents for our consideration, upon its con- cave under surface, a coating of epithelial cells already long kjioAvn. The latter are narrow, cylindrical, and nucleated; in length 00226-0*0338 mm., F 258—Dental sac of a tolerably mature humi.n and in breadth 0*0451 mm. The frctus, partly diagrammatic a fibrous wall of the , , „ , . , e , sac with its external stratum a\ and internal a , whole of this layer Avas formerly b enamel organ, with its papillary and parietal ccllsc; nr,UaA f*h0 onnmiJ mnmhrnvr <>• enamel membrane and enamel prisms; /dental callea tne enamel memoranc. • ^ wjth .fg capil]aries g. continuation of the con- The epithelium, on the Other nective-tissue of the parietes into that of the dental hand, which clothes the external eerm. _ convex surface of the enamel organ (b), was only genera ly recognisedI at a later date. It consists of low cells, measuring in man 0*01 Id mm. (.) The last-named coating, however, does not by any means eyeryAvhere possess the same thickness : it forms, rather, numerous small bud-like 270 MANUAL OF HISTOLOGY. growths toAvards the follicle, especially at that portion covered by the gum. These interdigitate with the vascular tufts just referred to. We have already considered, in § 116, the gelatinous non-vascular tissue enclosed in the cellular tunic of the enamel organ, so that Ave refer the reader again to what was there remarked. The dental germ (f) appears to be formed of an undeveloped connective- tissue, of a finely granular dull mass, containing a multitude of roundish nuclei and cells of like shape, or more or less fusiform. It is, moreover, highly vascular, the capillaries being recognisable at a short distance from its surface, forming numerous terminal loops (g, and fig. 258). Numerous nerves are also formed in it subsequently, Avhose origin calls for more accurate investigation, as also the question as to the occurrence of lymphatic vessels. The dental germ is covered by delicate cells arranged in strata, noiv more or less cylindrical, now of irregular figure (fig. 258, e ; 259). These are the dentine cells or odontoblasts, whose nature and position in the per- fect tooth has already been treated of in § 151. They correspond to the osteoblasts of Gegenbaur, which we have seen in the bony tissue (§ 147). These cells, taken as a Avhole, have been described as the " ivory or dentine membrane." Remarks.—1. These villous projections Avere first seen by English investigators (Huxley, Goodsir, Todd, and Bowman, 11. cc), and then more accurately described at a later date, principally by Robin and Magitot. 2. The epithelium on the outer surface of the enamel organ was also first recognised by English observers (Nasmyth, Huxley); but the French have made it an object of closer study ; comp. Guillot, I. c, Robin and Magitot (Journ. de la physiol., Tome 4, p. 71). §155. The dental germ is now destined, with the odontoblasts, to produce dentine. To this end the elements in question send out long filiform 'tictuc^^ SST^tlvoTce^ SSKT *T ™ ?«*"* called membrana prceformativa. V ' U"d dentine c; * en»mel; e, so- processes externally, which constitute the soft dental fibres of Tomes already known to us from § 151. Between them a homogeneous substance hen makes its appearance, whose origin must be accepted a being similar to that of the intercellular matters of the connect vettsu TISSUES OF THE BODY. 271 group. This is converted into dentine by a diffuse calcification similar to that of the so nearly allied osseous tissue; while the walls of the canaliculi of the teeth are formed by the bounding laminae of the mass sur- rounding the fibres of Tomes. The following sketch may be accepted as toler ably faithful as far as Ave are acquainted Avith the course of development, so difficult to follow. Young dentine cells (fig. 259, b; fig. 260) present themselves as membrane- less nucleated structures closely crovvded together, and of irregular jagged form, and united one with another by means of short processes. Exter- nally, they send off single or multiple prolongations, which form interlacements by means of side branches with the processes of adja- cent cells. The odonto- blasts eventually become longer and narroAver, and the more peripheral portions of their processes attain a considerable length. Thus are formed the soft fibres of Tomes. The calcification already mentioned commences at the apex of the dental germ, in the tissue just described, in the form of a single, or frequently, at first, of several separate thin plates. This plate has been named the "dental cup" (Zahnscherbchen) (fig. 259, c). On the further superficial extension of this structure the calcified layer spreads doAvn over the sides of the dental germ, in Avhich, Avith the commencement of calcification, the vascular netAvork has already reached its fullest development. But, owing to the continued production of the fibres of Tomes, of the canaliculi and the ground-substance, through the agency of the still soft ivory cells beloAv the dental cup, and the progressive calcifica- tion of the ground-substance, the thickness of the dental germ decreases more and more, although it has groAvn considerably in length. This increase in length leads eventually to the formation of the root, which is changed into ivory exactly in the same Avay as the croAvn, and becomes calcified externally. The production of the cement commences before the passage of the teeth through the gums, as soon as the root is developed. But the bony mass in this case arises, it is supposed, from a growth of the inferior portion of the dental sac, the latter becoming converted into osteogenic substance, as in the growth of the periosteum, and undergoing diffuse calcification. Osteoblasts and bundles of connective-tissue are also to be Fig. 2C0.—Dentine cells after Lent. At a and b, simple filiform processes, which become converted into canaliculi; c, rf, specimens ofthe latter with branches; e, fusiform cell; and /, one of the latter undergoing division. 272 MANUAL OF HISTOLOGY. seen here, the latter reminding us of Sharpey's fibres (§ 142) in the Avay in Avhich they ossify. According to this description, both parts have a similar or identical nature to that of osseous tissue. Dentine represents a modified bony substance, and the cement is deposited upon it in the same manner as a younger periosteal layer upon an older, while the communications between the canaliculi of the tooth and those of the bone occur in a Avay analogous to that taking place in concentric growth of bone. Just as the cement is formed around the root, so is the enamel laid down upon the croAvn as a coating closely adherent to the subjacent mass. The elongated tooth then presses gradually against the enamel organ and roof of the dental sac until these disappear Avith the super- imposed gum. Thus the eruption of the twenty milk teeth comes to pass, Avhich begins in the sixth or seventh month of an infant's life, terminating at about the commencement of the second, or sometimes in the middle of the third year. The residue of the dental follicle persists as the periosteum of the alveolus. Around the milk teeth, which have been already protruded, it forms a system of obliquely ascending fibres passing from the edge of the alveolus to the neck of the tooth {ligamentum circulare dentis of Koelliker). The external epithelium of the enamel organ may, perhaps, persist also in the form of the " enamel cuticle." The subsequent falling out of the milk teeth is preceded by re-absorp- tion of their roots. The successive eruption of the thirty-two permanent teeth commences in the seventh year, lasting until the end of the second decade, when the Avisdom teeth make their appearance. The cause of the falling out of the teeth at an advanced age has not yet been sufficiently cleared up. It is probable, however, that a narrow- ing of the canaliculi, and degeneration of Tomes' fibres, prepares the way for the decay of the organs. The origin of dental caries requires also further investigation. In it Ave remark in succession, softening and destruction of the enamel mem- brane and enamel, of the dentine in its ground-substance, and of the dental sheaths and fibres. In this process vibriones and filiform fungi make their appearance. The so-called tartar of the teeth consists of albuminates and allied matters from the fluid of the mouth, together Avith a large proportion of phosphates. The former amount, according to Berzelius, to 21, the latter to 79 per cent. Hypertrophies of various external portions of the teeth are of fre- quent occurrence: they generally affect the cement or dentine, or both together. There likewise occurs frequently enough a neAv formation of dentine on the internal surface of the tooth and an ossification of the pulp. To compensate foi the wear and tear of the croAvn also, produced by chewing, and also of loss of substance on the external surface through disease, there are neAv layers of dentine laid down by the pulp on the interior of the central cavity. Teeth which have been drawn may again become attached, and healed in their alveoli on being replaced. The formation of teeth in strange localities occurs also as a rarity, especially in the ovary, but occasionally in other situations. TISSUES OF THE BODY. 273 Remarks.—1. Here we meet with two different views, as in considering bone and connective-tissue. According to one of these, dentine arises from the odontoblasts in the form of an intercellular substance produced by the latter; according to another, a direct calcification of these cells takes place. The latter theory has been defended recently, principally by Waldeyer:—" The formation of dentine consists in a trans- formation of part of the protoplasm of the ivory cells into a glutinous substance, which becomes subsecpiently calcified, after which the other unchanged part of the body of the cell remains over in the hardened mass in the form of soft fibres." 2. Besides diffuse calcification, the laying down of the dentine globules takes place at this period. These are small spheroidal calcified bodies, which are supposed to be partly permanent (p. 262), and partly to disappear subsequently. Hoppe maintains that they are not simple concretions of the bony earths with an organic collagenic substratum, as has been already mentioned. He Avas unable to convert their organic substratum into glutin by boiling. He is rather of the opinion of Hannover, that their nature is cellular. In the interstices incompletely calcified appearing between them, again we have the "interglobular spaces" touched on in section 150. 3. See Trans, of the London Pathol. Society, vol. vii., p. 185. Earlier numbers also of this periodical contain other important works of the same author on the diseased states of the teeth. D. Tissues composed of Transformed and as a rule Co- hering Cells, with homogenous, scanty, and more or less solid Intermediate Substance. 12. Enamel Tissue. §156. Enamel, which in the human subject is confined to the teeth, as also among the higher animals, and which is, as we shall find further on, a decidedly epithelial production, presents a glistening white appearance like porcelain, but may also be met with of a more or less yelloAV or bluish tint. Its surface appears at first quite smooth, but by the help of a lens we may usually discover a number of delicate grooves encircling the crown, of which Retzius counted 24 to the 1 mm., and Avhich become more frequent down beloAv near the edge of the cement. Like tho osseous coating of the dentine, the enamel is thinnest at the neck of the tooth, where it is sharply defined against the cement. From this point upwards it becomes stronger, at- taining its greatest thickness in the middle of the croAvn (comp. fig. 250, p. 261). Examined with polarised light, enamel displays much more double re- fracting power than either dentine or cement (Hoppe, Valentin). From the examination of finely ground sections, or of small portions of enamel macerated in acid, we gather, that the tissue (fig. 261) consists of long polyhedral fibres or pillars, closely crowded together, ^ 2C1.__ vertical SIC- and held thus bv a scanty amount of some cement- tionofenamei.wiihsub- J v jacent dental tissue, ing substance. from the human tooth. These are called " enamel columns or prisms." "^^ZTV ^ They o-enerally extend through the whole thickness terstices between these of the enamel layer, resting Avith one end on the den- latter^ dentine with tine, Avhile the other assists in forming the surface of the former. It is possible, however, that shorter prisms also occur, which terminate at a greater or less distance from the dental tissue Their transverse diameter lies between 0*0034 and 0*0045 mm., and 274 MANUAL OF HISTOLOGY. their direction roughly taken corresponds to that of the canaliculi of the tooth. If a transverse section of the enamel layer be made, the cut prisms appear like a delicate tesselated pavement of four or six sided plates, reminding one of epithelium (fig. 262). Finally, the enamel is coated and protected by an extremely hard and resistent homogeneous membrane discovered by Nasmyth (fig. 261, a). This is the so-called "enamel cuticle" or cuticula dentis (Koel- liker). Its thickness is about 0-001-0*0013 mm. Fltf. 262. — Transverse section of human enamel prisms. §157. Nearer inspection discloses to us many peculiari- ties in the texture of enamel. Owin-? to the fact that certain groups of the prisms project deeper into the surface of the dentine than others, the latter becomes rough and uneven. Further, a question arises whether the prisms do not increase in breadth externally, since the internal surface of the layer appears to be less extensive than superficial, and since no considerable interstitial sub- stance can be detected; or whether a certain number of the prisms, shorter than the others, may not terminate at some distance from the surface of the subjacent dentine. The occurrence of such short pillars has been supposed by many, although it is hardly possible to decide the question owing to their unsteady course. Czermak states, however, that he has often observed a widen- ing of the columns externally. The latter (fig. 263) display as a rule, in vary- ing clearness and distance, a transverse linear mark- ing, Avhich may be partly dependent perhaps upon the progressive laminar calcification of the struc- ture (Hannover, Hertz). /\ Ml\((f M Finally, as to the direction of the individual \y ™ v prisms, we find it very variable; owing to their undulations and different bends, whole groups of them may intersect others. Thus in longitu- dinal sections, the prisms are cut through, in part longitudinally, in part transversely and obliquely, and so communicate a streaky appearance to the surface. Enamel possesses no special nutritive canals. But a system of acci- dental cavities is met with in it (fig. 261, c), Avhich vary greatly in magni- tude, and are sometimes simple, sometimes branched, mostly elongated in a direction parallel to that of the prisms: they may, hoA\*ever run obliquely also. They are usually situated in that portion of the enamel tissue nearest to the cement. But rents and cracks resulting from the grinding of sections may give rise to the same appearances. °Finally, it seems probable that some of Tomes' fibres penetrate with their canaliculi from the dentine into the substance of the enamel, as already mentioned and run here for a short distance betAveen the prisms, either sinking into the cavities or coming to an end among the prisms. Remark.—Comp. Tomes' work (Phil. Transact.), p. 522. Fig. 263.—Pieces of human enamel prisms. TISSUES OF THE BODY. 275 § 158. This substance enamel, noAv under consideration, is the hardest and densest in the body, and admirably suited for the protection of the sub- jacent dentine. In this respect, hoAvever, the prisms are excelled by the enamel cuticle. As far as we know of the chemical constitution of this tissue, it is the poorest in Avater of any in the system, and most rich at the same time in inorganic constituents. For every 2, 4, or 6 per cent, of organic matter which retains the form of the prisms after treatment with acids, but Avhich yields no glutin on boiling (Hoppe), we find 81-90 per cent, of phosphate, 4-9 of carbonate, and more than 3 per cent, of fluoride of calcium (according to Berzelius); also 1*5-25 of phosphate of magnesium. We shall take as examples the two folloAving analyses of Bibra, of which the first refers to the enamel from the molar tooth of an adult man, and the latter to that from a woman of twenty-five years of age ;— Organic substratum, Fat, ...'.. Phosphate and fluoride of calcium, Carbonate of calcium, Phosphate of magnesium, Other salts, .... Partially developed enamel is naturally far richer in organic constituents. The substratum of organic matter found in the enamel cuticle is remark- 1. 2. 3*39 (1) 5.97 0*20 traces . 89*82 81*63 4-37 8-88 1-34 2-55 0*88 0*97 Fig. 264. able for its poAver of resisting acids and alkalies. It yields, moreover, no glutin (Koelliker). The development of enamel takes place, as has long been knoAvn, from the cells clothing the concave surface of the enamel organ (fig. 258, c), and in such a Avay that each future prism corresponds to a cell. The process is, however, still a matter of controversy, although everything seems to point to the conclusion that a calcification of the bodies of the cells take3 place. As we are already aware, the latter at first appear in the form of cylin- drical structures, with vesicular nuclei and very delicately granular con- tents, and of about the same breadth as the prisms. Later on, as the 276 MANUAL OF HISTOLOGY. calcification of the dentine is commencing, Ave may remark the surface o» the latter covered with already hardened but still short prisms (fig. 264, d). Not seldom Ave encounter appearances as if over these prisms there were superimposed a special cuticle, the so-called membrana praiformativa (fig. 264, e). Such a membrane does not in reality exist however, and the whole is only a deceptive appearance produced by the youngest layer of enamel which is undergoing development, and Avhich may often be raised off in the form of a membrane (after the decalcification of the whole) from the fully formed tissue beneath. 13. Lens Tissue. §159. The crystalline lens (1) consists of a capsule enclosing a tissue formed of extremely fine transparent fibres or tubules. The latter have had their origin from the cells of the corneous embryonic plate, and the Avhole structure bears a decidedly epithelial character. The capsula lentis (fig. 265, a) is a perfectly transparent membrane, apparently structureless, and only under very high magnifying power finely streaked. It is much thicker anteriorly than posteriorly (about 0*0135-0*0068 mm.). The inner surface of the anterior half of the capsule is lined with flattened epithelium of simple nucleated cells, already mentioned § 87. These measure from 0*0169 to 0*0226 mm. in diameter (tig. 265, b, and 269, d). In the neighbourhood of the zonula Ziunii this epithelium passes at its external border into a zone of young cells with multiple nuclei and but little cell body; here also the thickening of the capsule ceases. Nearer still to the circumference we encounter (springing from these formative cells) roundish nucleated ele- ments, destined, to be transformed into the fibres of the lens (Becker). The fibres of the lens or "lens tubes" (Linsenrbhren) (fig. 266, a, b) are pale and transparent, Avithout any further structure in their interior. In the most external layers of the lens they are especially trans- parent, and measure in breadth 0*0902- 0*0113 mm., Avhile in the central portion of the organ they are finer (0*0056 mm.), but more distinctly bounded and clearer. The fibres at the periphery (d) possess a viscid homogeneous contents, probably enclosed in a very delicate envelope, and deserve, therefore, rather the name of tubes. Those of the interior (b), on the other hand, have become more solid, and not unfrequently present a serrated appearance along their border, a condition of great significance, for the adhesion of the several tubes one with another, especially among fishes, where these edges are regularly toothed. ° As may be seen even from side views, the fibres of the lens are not Fig, 265.—Diagrammatic sketcli of the human lens, a, the capsule; c, the fibres of the lens, with widened ends, d, applied to the anterior layer of epithelium b, and abutting behind against the capsule e; /, the so-called nucleus zone. TISSUES OF THE BODY. 277 Fig. 266.—Fibres of the hu- man lens, a, from the cir- cumference; and 6, from the more central part. cylindrical, but more or less flattened (fig. 266, a). This is, hoAvever most evident when we take the transverse section of a dried lens (fi<*. 267N for our object. Here we find fhe several tubes most delicately marked out as compressed hexagonal figures, measuring 0*0113-0*0056 mm. in breadth. Looking now to the arrangement of the fibres (fig. 265), we find them placed meridionally, pass- ing from the middle portion of the anterior half of the capsule over the equator of the organ to a corresponding point on the posterior half. Their broad surfaces are always directed outwards, and their borders are closely applied to those of ad- jacent fibres. OAving to the latter union being the stronger of the two, Avhole layers of fibres can be peeled off from the lens in the form of delicate concentric lamellae, which follow at the surface of the organ the greater curves of the latter, while within they are more circular. In perpendicular sections of hardened lenses the fibres (fig. 265, c) are seen to spring up with a broad extremity (d) under the epithelial coat- ing (b) of the anterior wall, and then, pursuing their curved course, to end in a similar manner by insertion into the posterior half of the capsule (e), which is devoid of cells (2). In following up this course of the fibres, we remark in the neighbourhood of the equator of the organ, in each, a beau- tiful rounded vesicular nucleus (/), about 00074-0 0129 mm. in diameter. A glance through the transparent tissue down upon this arrangement of the nuclei, the " nucleus zone," of H. Meyer, is one Avhich well repays the observer for the trouble of preparation. The statement, hoAvever, that each fibre of the lens possesses only one nucleus is not correct in all cases (see beloAv) : in a foetus of eight months old I myself have seen them Avith tAvo or three, most distinctly visible (fig. 270). We must not, hoAvever, picture this nucleus zone to ourselves as a diaphragm occupying the equatorial plane; it resembles far more a leaf attached at the periphery, Avhich is continued inwards in an undulating course, at regular distances from the rays of the " lens star," to be referred to immediately (von Becker.) The cloudy organ of the infant (fig. 268) presents for our consideration a very peculiar arrangement in its structure in the relations of the so-called '* lens stars." In the centre of the anterior sur- face (a), namely, Ave perceive three bands meeting together at an angle of 120°, forming a three-rayed star or inverted Y. On the posterior wall, either a similar figure reversed is met with or that of a four-rayed star (b). In the first case the arms of the posterior Y occupy a position in relation to the anterior as though turned on their axis to the amount of 60°. Later on in life each of these rays subdivides at acute angles into regular series of branches, giving rise to complicated stellate figures. The microscope teaches us that within such a ray and its system of Fig. 267.—Transverse sec- tion of the fibres of a dried lens. Fig. 268.—Lens from an infant, a, the anterior; b, the posterior surface. 278 MANUAL OF HISTOLOGY. branches there exists no lens fibres, their place being occupied by a tena- cious homogeneous mass. Thus we see that the organ in question is divided by a system of partitions, springing Avith its layers from a central space in the lens; in that this substance can be folloAved through the latter in the form of septa. The fibres, therefore, form in each half of the lens some three or four wedge-shaped pieces. This arrangement naturally determines the course of the fibres, and makes it impossible that any one of them should actually reach both poles. Remarks.—1. Beside German handbooks on histology and monographs, comp. Bowman, Lectures on the parts concerned in the operations of the eye, etc., London, 1849 ; Th. Nunnely in the Journ. of Microsc. Science, 1858, p. 136. 2. These broadened ends of the fibres of the lens may simulate Avhen in transverse section a flattened epithelium, without nuclei however. It was formerly supposed that there existed between the lens and capsule a small quantity of a clear thick fluid, the humor Morgagnii. This is not, however, present in the living eye, and is the result of a post-mortem change, produced by the decomposition of the so delicately con- stituted peripheral fibres and epithelium. The latter swells up before bursting into a number of spherical globules (fig. 269, e). § 160. Turning now to the composition of the tissue of tlie lens, that of the capsule, in the first place, is at present but insufficiently known. Thn latter gelatinises in acetic acid and solutions of the alkalies, without, how- ever, becoming clouded or dissolved. Even after tAvo days' boiling, also. it is not converted into glutin. It offers prolonged resistance to the action of alkalies, but is, on the other hand, gradually dissolved in the mineral acids (Mensonides). Thus we have the reactions, to a certain extent, of most of the transparent elastic membranes. On the other hand, according to Strahl's statements, each capsule may be dissolved by boiling for several hours in water, yielding a substance which does not give, hoAvever, the reactions of glutin. The composition of the nuclei and walls of the lens fibres is not as yet known. In their interior is contained a concentrated solution of a peculiar and very unstable protein substance knoAvn as crystallin (§ 12, p. 17). Owing to its close relationship to albumen, all reagents which cause the latter to coagulate produce clouding in the tissue of the lens, and when suitably employed may render the structure of the latter more distinct. In this respect chromic acid has gained great repute. Besides this, the lens contains a not inconsiderable proportion of fats, and, according to older analyses, of extractive matters also. For the human lens Berzelius obtained the following percentage, of Water, . . . . . 58*0 Protein matter, ..... 35-9 Walls of the fibres, &c, remaining on the filter, . 2*4 Extractive matters, ... 3.7 The proportion of fats in the human lens Avas found to be 2-06 per cent. (Husson); among them cholestearin is present (Lohmeyer). The amount of mineral constituents met Avith is only 0-35 per cent. The clouding of the lens after death depends upon some change in composition not yet understood. The specific gravity of this organ in the human being is, according to Chenevix, 1*076 in the external layers, while that of the more dense TISSUES OF THE BODY. 279 nucleus may reach IT94. The index of refraction amounts, in the external strata, to T4071 according to Krause; in the middle to 1*4319, and in the central to T4564. §161. The lens is developed from a doubling-in of the superficial layer of cells coating the embryonic body or the corneous layer, which has been already discussed in considering the epidermis. But even at a very early period it appears as a structure completely sepa- rated from the layer just mentioned. It is hollow in the interior, and has very thick walls, which are bounded by a transparent membrane. These walls are formed of several strata of elongated cells. From them, possibly, the excretion of the homogeneous substance has taken place, which subsequently solidifies into a capsule for the whole organ. In our Fig. 269.—«-«, Cells from the lens of a foetal pig two inches long, a, original cells; 6, other elongated specimens; c, some more so still, passing into the form of tubes; d, epithelium of the lens of a human embryo at eight months; «, cells from the so-called humor Morgagnii.* Fig. 270.—Fibres from the lens of a human foetus at eight months, a, flbies with one nucleus; 6, unother, which still shows its cellular character; c, flattened form, as seen from the side; d, fibres with two or three nuclei. opinion, however, the capsule is a modified deposit from the adjacent connective-tissue. These cells gradually fill up, it is supposed, with their descendants, the central cavity, and become developed in most cases into lens tubes or fibres, while a certain remainder only, preserving their original characters, constitute the epithelium of the capsule seen on its anterior internal surface. In young embryos Ave have an opportunity of studying the fibres of the lens in process of development (fig. 269, a-e). In more advanced foetuses, as for instance in the human towards the 19 280 MANUAL OF HISTOLOGY. last months, the fibres are quite similar to what are found in the adult (fig. 270, a, c), at times, however, still preserving the cellular character (b). Not very unfrequently Ave encounter also lens fibres with double or even triple nucleus (d). The further production of these tubes probably takes place by a process of segmentation of the immature cells in the zone situated at the border of the epithelium of the capsule (§ 159), the new elements being laid doAvn over the older ones. That the process and the growth of the lens extend far beyond the period of intra-uterine life is almost a matter of certainty. At an early period the capsule of the lens is enclosed in a vascular membrane, which forms a part of the well known system of envelopes of the organ under the name of the membrana capsulo-pupillaris. After birth the number of the fibres of the lens is multiplied with the growth of the body, but their diameter is not increased. They take their rise from the epithelial cells of the capsule, and, in keeping with the character of epithelial structures, can be regenerated provided the capsule and layer of cells be preserved. It is not difficult to conceive that a lens formed after the capsule has once been opened never attains the same regularity of form as the first structure, seeing its figure is quite dependent on that of the capsule. The amount and nature of the interchange of matter going on in this organ is not yet known. The former is probably not entirely insignificant. 14. Muscle Tissue. § 162. The muscles, springing from the middle embryonic plate, are made up Fig. 271.—Striped muscle-fibres. Fig. 272.—Elements of smooth muscle, from the rabbit. nie rauoit. of a soft reddish fibrillated tissue, which is remarkable for the property it possesses of contracting Avhen its motor nerves are excited This necu- harity is characterised by the term irritability. As we are tau-ht by TISSUES OF THE BODY. 281 physiology, the contraction of muscular tissue is of tAvo kinds, voluntary and involuntary. Viewed from a histological point of vieAv, muscles may be divided into those Avhich are made up of long transversely striated fibres as elementary structures (fig. 271), and those built up of smooth or unstriped fusiform elongated cells (fig. 272). Dependent on these differences we speak of striped and smooth muscle. This anatomical difference, hoAvever, seems at first sight much greater than it is in reality. In the first place, we encounter many intermediate forms between these two species of muscular tissue in the animal Avorld; and, secondly, the history of development has recently shown that both elements have an origin extremely similar, namely, each form a single cell (§ 59). The element of the unstriped tissue preserves this character throughout life, the striped fibre forsakes its original nature in the greater complication of its development. In conclusion, we need only remark that the voluntary muscles of our body consist of striated fibres (the heart, hoAvever, also, among those organs Avhich are involuntary), whilst those muscles Avithdrawn from the influence of the Avill are composed of smooth fibres. The expressions, therefore, of "smooth" and •'involuntary," or "striped" and "voluntary," do not correspond exactly in the human body. The specific gravity of the first of these Avas settled by Krause and Fischer to be T058, that of the latter 1*041. §163. The elements of unstriped muscular tissue (fig. 273) were formerly held to be long, pale, band-like fibres (i), displaying at intervals several like- Avise elongated nuclei. It remained for Koelliker's quickness of perception to recognise in these fibres a series of elongated cells arranged linearly one after the other, and in the year 1847 to introduce to the notice of his- tologists the " contractile fibre-cell" (c-li),—a great step toAvards a proper comprehension of the structure of this tissue, so difficult of investigation. "We usually meet Avith the smooth muscle-cell in the form of a long (d-f) band, which may at times possess extremely great length (g), and which generally runs off to a point at both ends. It is often short however (c). Its medium length is about 00451-0'0902 mm., short cells measuring often 0*0282 mm., and very long specimens 0*2256 mm. and upAvards. Its breadth lies between 0*0074 and 0*0151 mm. Further, it appears pale and homogeneous, either completely colourless or tinged slightly yelloAV, and without recognisable difference between the envelope and contents. Not unfrequently Ave may remark a row of granules, the residue of the earlier protoplasm, extending from each pole of the nucleus into the body of the cell (fig. 272, a); small dust-like molecules of the same may also cloud the otherwise clear substance of the cell. Finally, as a sign of retrograde metamorphosis, we find fat granules in varying quantity and size (fig. 273, h). The contractile fibre-cell may present a very characteristic appearance, principally due to its nucleus, which appears under the action of strong acid as a tolerably pale, long, cylindrical rod, more or less rounded at both ends. Again, this nucleus is met with quite homogeneous, Avithout any difference of contents and envelope, and apparently Avithout any nucleus. Its medium length is 0*0226 mm., and breadth 0*0023-0*0029 mm. Its 282 MANUAL OF HISTOLOGY. situation is generally at an equal distance from both ends and in the axis nf tbl eel as may be best seen in transverse sections of previously dried mu£M& fro^ which, also, we may convince ourselves of the cyhn- drical form of most of the fibres. In most cases the nucleus is only single; but two, three, or even four, may occur in one ced (Remak, Koelliker, G. Schwalbe),— a circumstance of great importance in tracing the relationship of these to striated muscle fibres. It is only very lately that, by the aid of more advanced technical know- ledge, we have been enabled to render visible in many nuclei, single or mul- tiple (1-4), granules of round form and glittering appearance, which have pro- bably the significance of nucleoli. Their diameter is 0*0009-0*0002 mm. (Hessling, Frankenhduser, Arnold, Schwalbe). I Under the polarising microscope I I B H 1 ft(iid&jil tne contractile fibre-cell is found to V \V |K^ 1 ll fS: ^e double refracting and positive to the axis (Valentin). But though this cell appear thus singular in a state of maturity, it bears in the embryonic body a less striking character; the nucleus is then round and vesicular (a, b). Whether this original constitution may not per- sist in many parts of the body is a question incapable at present of being answered. Besides this, it is impossible to indicate any very certain features of distinction between the fusiform cells of connective-tissue, which are like- wise endowed with vital contractdity, and the elements of smooth muscle. The many controversies which have taken place in the last few years as to whether we are to admit the presence of contractile muscle cells in this part and that, or no, must be judged accordingly. On the other hand, the singly nucleated contractile fibre-cells may acquire striated contents, and thus approach nearer to the eleihents of voluntary muscle. Among such may be reckoned the elements of the muscle of the heart of lower vertebrates (Weismann), of the bulbus aortae of the salamander and proteus (Leydig); but probably not the fibres situated under the endocardium of the ruminants, of pigs and horses, bearing the name of the fibres of Purkinje. Smooth unstriped muscle is to be found throughout the whole diges- tive tract, from the inferior end of the oesophagus down nearly to the Fig. 273. — Smooth muscle fibres from the human being and other mammals, a, a for- mative cell from the neighbourhood of the stomach of a foetal pig ten inches long; 6, another more developed; c-g, various forms of contractile cells from the human body; h, one of the latter, containing fat granules; t, a bundle of smooth muscle fibres; k, a transverse section through one of these from the aorta of the ox, with several nuclei in the plane of the cut. TISSUES OF THE BODY. 283 termination of the rectum; it is met with also in the mucous membrane itself, as the so-called muscularis mucosve, in the form of thin layers and small bundles. The organs of respiration are likewise supplied with this tissue: thus, it is seen in the posterior wall of the trachea, in the circular fibres of the bronchi and their branches, and perhaps also in the pul- monary vesicles. The walls of blood-vessels possess it also, especially in the middle layer of their coats. These contractile cells make their appear- ance too in the cutis: firstly, in the form of small groups, as in the hair follicles, the sebaceous and sudoriferous glands; and then again forming more or less continuous layers, as in the tunica dartos of the scrotum, the mamma, and areola. The human biliary apparatus only shows tissue in the walls of the gall bladder (Henle, Eberth). Further, the tissue is distributed throughout the urinary apparatus. It occurs in the calyces of the kidneys in the form of continuous strata, and also in the pelvis of the latter organ, in the ureters and vesica. Again, in the form of scattered elements along the urethra and over the surface of the kidney. In the male organs of generation also it is extensively met with: thus, in the tunica dartos, between the tunica vaginalis communis and propria ofthe cord, epididymis, vas deferens, seminal vesicles, prostate, Cowper's glands, and corpora cavernosa. Also in the female: thus, in the ovaries, in the Fallopian tubes, and uterus, which latter organ presents to us during pregnancy the greatest accumulation of the tissue in question Avhich exists in the body. Again, in the round (Koelliker) and broad ligaments (Luschka), and in the corpora cavernosa. Further, smooth muscular fibres are supposed to exist in the envelope and in the septa within the spleen and lymphatic glands of mammals. Finally, they occur in the organs of vision as sphincters and dilators of the pupil; also in the choroid, in the cdiary and orbital, as well as eyelid muscles (H. Muller). §164. The second species of muscular tissue, namely, the striped or striated, is to be found in all the muscles of the trunk and extremities, —those of the ear and external parts of the eye, with the exception of the muscles mentioned in the preceding section. It enters further into the construction of many internal organs, as the tongue, pharynx, upper portion of oesophagus, larynx, genitals, termination of the rectum, and diaphragm. Finally, it presents itself, modified to a certain extent, in the heart. As elements, we here meet Avith long cylindrical and strongly flattened fibres (fig. 274, 1), which do not, as a rule, give off branches. They have a thickness of from 0*0113 and 0*0187 mm. up to 0*0563 mm. in the human body. To these the name of " muscle fibres " or " primitive bundles " has been given. The human primitive bundle, which is, owing to its greater thickness, of a yelloAver tint than the smooth element, dis- plays, in contrast to the latter, a most striking and characteristic texture under high magnifying power. It consists of an envelope and contractile contents. The first of these, called usually the " sarkolemma " or " primitive sheath," is a transparent, homogeneous membrane, which, on account of its high degree of elasticity, ahvays remains closely adherent to the included mass in all the changes of form which take place in the latter (fig. 274, 1). The primitive sheath may be demonstrated apart from chemical aid by simply break- ing the Continuity of the contents (2 a), or also, as is strongly recom- mended, by treatment of the living fibre with water, on which the 28-4 MANUAL OF HISTOLOGY. membrane becomes raised up in blebs by endosmosis. Preparations also of the muscles of naked amphibia Avhich have lain in spirit frequently afford very good objects, in which the envelope is observed widely sepa- rated from the included mass. On the internal surface of the sarkolemma" are situated a series of roundish or oval nuclei (1 d) 0*0074-0*0113 mm. in length. More minute examination of the muscle fibres of naked amphibia (fig. 275) Avith very high magnifying powers shows the nuclei (c) to be vesicular, with tolerably thick, and therefore doubly contoured walls, and to contain one or two nucleoli. In fresh tissue the nucleus lies closely enveloped in a fusiform cleft. The apices of the latter are occupied by a homo- geneous clear substance. This is tho remainder of the original proto- plasm, Avhich has not been consumed in the formation of the fleshy matter of the fibre. This, taken as a Avhole, has been named the "muscle Fig. 274.—1. Striated muscle fibre with a Fig. 275.—A muscle fibre from the frog, breaking up into primitive fibrillse a; more magnified 800 times, a, dark zones with distinct striation at 6, and longitudinal lines sarcous elements; 6, lighter zones; c, at c; d, nuclei. 2. A fibre, b, torn through nuclei; d, interstitial granules. (Alcohol at a, with tlie sheath partially empty and preparation). visible. corpuscle" (M. Schultze, Welcker), and is looked upon as equivalent to a cell. In fig. 275 we may remark filiform streaks springing from these muscle corpuscles, and dotted with fat granules throughout, as also is the degenerated body of the cell. These we shall have again to take into consideration below. The number of these nuclei or muscle corpuscles is not inconsiderable; their position is sometimes Avithout arrangement, sometimes alternating. In the fibres of the heart alone do there exist, beside the circumferential nuclear formations, others Avhich occupy the axis. But among the lower TISSUES OF THE BODY. 285 animals, as for instance in the frog, the nuclei lie at every depth in the fibre. The contents enclosed in the sarkolemma, or the fleshy substance of the muscle (fig. 274, 1), is of extremely complex and delicate texture. It presents, but in varying degrees of distinctness, a longitudinal (c) and transverse striation (d), affecting the whole thickness of the fibre. In many dead muscles the longitudinal marking may be observed with the greatest clearness in many fibres, appearing in the form of very delicate but distinct parallel lines, traversing the Avhole length of the element. The distance of these from one another varies between 0*0011-0*0022 mm. In many cases the lines run continuously for a considerable dis- tance, but more frequently only make their appearance at intervals in the fleshy mass, and, after running a short course, disappear again. On transverse sectious of a fibre we may frequently observe the sub- stance of the contents projecting in the form of fine fibrillse or bands (1, a), bounded by the linear marking. The objects, however, which Ave obtain by the action of certain reagents on the muscle fibres are extremely peculiar,—a method of treatment much in use. Those Avhich have been macerated in cold or boiled in hot water, such also as have been subjected to the prolonged action of alcohol, bichloride of mercury, chromic acid, and, more than all, of bichromate of potash, are often seen split up in the most beautiful Avay into long fine fibres of 0*0011- 0*0022 mm. in breadth (fig. 276). Owing to this circumstance, it lias bppn SUUOOSed bv manV Fta- 276.—A muscle fibre after the continued action of It nas Deen SUppobeu uy uiauy bichromate of potash for twenty-four hours, showim? that the fibres of muscle are its partial resolution into fibriUse. made up of fine elementary threads or " muscle fibrillsB," as they have been named ;^ the muscle fibres are also known, on this account, as " primitive bundles." The theory in question has had among its defenders a number ot men Avhose opinions should have great weight. Among these we may mention Schwann, Valentin, Henle, Gerlach, Koelliker, Leydig, Welcker, Schon. Remarks -Comn. beside Henle's work, Bowman in the Phil. Transact. 1840 Parti t" ». ^d 1841, Part 1, p. 457 ; also the two articles by the same, " Muse e and "Muscular Motion," in the Cyclopedia, vol. m. p. 506 and 519 ; and in tht work edited in conjunction with Todd, vol. l. p. 150. §165. The transverse striation of muscle is also subject to much variation, and it is a matter of great difficulty to gain a proper conception of it, owing to the minuteness of the object and the obstacles in the way oi correct focus. In the first place, we meet with dark, sharply defined, and continuous lines, running parallel to one another, whether in a straight or undulating course. Their distance from one another likewise lies between 0*0011 and 0*0023 mm. Again, these transverse striae may be inter- rupted, ceasing for a certain distance. The contour of the whole fibreas: at the sanie time quite smooth. In other muscle fibres markings not so dark but much broader, are seen, regular cross-bands, so that the whole appears to consist of a double system of dark and light transverse zones, i mall), 286 MANUAL OF HISTOLOGY. though seldom, the transverse lines may become separated from one another, the lateral outlines of the fibre becoming indented; so that the whole conveys to us the impression that it is about to break up into a number of plates. Coincident with the more distinct appearance of trans- verse striation, the longitudinal marking usually decreases in clearness. "When treated with certain reagents the peculiarities of the tissue in this case also are forcibly brought before us. Thus, acetic acid causes the longitudinal lines to vanish, while the transverse remain a certain time still visible. In very dilute hydrochloric acid, and also in the acid gastric juice, the muscle fibre is resolved into a number of thin disks, while at the same time that it swells up, and commencing solution sets in, the longitudinal markings becoming completely destroyed. These disks often separate from one another in the most regular manner imaginable (fig. 277, 4, 5). Carbonate of sodium has a similar action, but does not produce swelling of the tissue; chloride of calcium also, which, however, gives rise * to a shrinking and transverse wrinkling in the fibre, and not unfrequently causes the appearance in its interior of transverse rents. Now, as in the former cases, we believed ourselves warranted in accepting with certainty the fibrdlated composition of the muscle fibre, so ought Ave now, seeing these effects produced by the chemical reagents just named, to look upon the latter as made up of a number of disks or plates arranged one over another (1). The theories broached by histologists as to this peculiar double mark- ing of the muscle fibre are naturally enough very various, owing to the obscurity of the subject. If we except a multitude of manifestly incorrect efforts at explanation, there remained for many years only two modes of viewing the matter, by which the nature of the texture could be interpreted, at least in its most important features. Hence both of the views in question found assailants and defenders. According to the first of these theories, alreadjr mentioned in the pre- ceding section, the fibrillar are the pre-existing essential elements of the fleshy mass, and remarkable for their jointed structure (fig. 277, 2). Owing to the fact that the transverse markings of all the fibrillae occur at the same intervals and lie one beside the other, a striped appearance is communicated to the whole fibre (1). It is not difficult to see that the appearances presented may be thus tolerably well explained, and Avhy it is that we sometimes remark a longitudinal and sometimes transverse striation to preponderate. On the other hand, the occurrence of disks, with absence of the longitudinal lines, is difficult of interpretation. The second theory, which has gained for itself in recent times a consi- derable circle of adherents, and Avhich we believed also, with certain modi- fications, to be correct, originated with that excellent English investigator Bowman. Among those who supported it, with greater or less modifi- cation, the names of Harting, Haeckel, Ley dig, Keferstein, Margo, may be mentioned. According to this theory, tho muscle fibre consists essentially of an aggregate of small particles (Fleischprismen, Fleischtheilchen), or sarcous elements, which, united in a transverse direction and clinging together, give the appearance of a disk or thin plate (Bowman's Disk, fig. 277, 3, 4, 5), and, arranged longitudinally, that of a fibril (1, 2). Both, how- ever, fibrds as Avell as disks, it was held, are not the optical expression of a pre-existing composition of the kind, which is entirely absent in the TISSUES OF THE BODY. 287 fresh, living muscle fibre; they rather indicate a tendency, on the part of the muscular element, to split up in one of these two directions (2). It must be adowed, however, that the tendency to break up into fibrillae in a longi- tudinal direction is greater than in the transverse into disks, the latter being of rarer occurrence than the primitive fibrillae. The supposition of the existence of these sarcous elements, connected longi- tudinally and transversely with one another, neces- sitates of course the pre- sence of a uniting medium between them. And when we remember the com- pletely opposite effect of the two reagents already mentioned, that, for in- stance, very dilute hydro- chloric acid resolves the muscle fibre into plates, while alcohol and bichro- mate of potassium convert it into fibrillae, we must look for two kinds of cement- ing substance,—one for the agglutination forming longitudinal fibrillae, and another different one unit- ing the flesh prisms in a transverse direction and forming disks. The quantity of transverse cement (probably more or less gelatinous) is far smaUer than that of the probably fluid longitudinal. The latter is remark- able for its great capacity for contraction and SAvelling out. In con- formity with this, we sometimes find the dark transverse zones placed far closer to each other than at other times. Here arose the very important question, how the closer relation of the sarcous elements to the transverse lines of the fibre was to be repre- sented. We frequently remark (and especially regularly after slight treatment with acetic acid) the transverse striation to be made up of dark zones, refract- ing the light very strongly, alternating Avith clearer belts of less refracting power. The latter are the layers of the longitudinal cement, SAVollen up and rendered clear; while the darker zones represent the sarcous elements, united together by an agglutinating medium, and forming disks. Accurate study of the effect of water acidulated with hydrochloric acid showed how the clear transverse zones become more distinct Avith the rapidly- commencing swelling up of the longitudinal cementing medium preceding solution; that a muscle fibre might then break up into disks, each of the latter consisting (like a voltaic element Avith its zinc and copper plate) of Fig. 277.—1. A muscle fibre with primitive fibrillae and trans- verse striation strongly marked, taken as the fundamental form. 2. Isolated fibrillae strongly magnified. 3. Sarcous elements united, forming a disk (diagrammatic). 4. Plates of human muscle after treatment with hydrochloric acid. 5. A human fibre after prolonged treatment with hydrochloric acid, with dark (c) and light (d) zones and nuclei (a, b). 6. Two pointed fibres from the human biceps brachii. From one of them the interstitial connective-tissue is prolonged over the end. 288 MANUAL OF HISTOLOGY. a darker and clearer portion (fig. 277, 5, c, d) (3); it showed further, that the clear part underwent solution by degrees, while the dark zone remain- ing over occasionally presented to vieAv the sarcous elements of a disk, as though in the act of separation from one another. The improved and greatly increased magnifying power of our new microscopes has since rendered it no longer difficult to obtain a vieiv of the fleshy prisms and of the fibrous structure of many muscles (fig. 278). The lamprey, and, better stdl, the lower amphibia (Proteus, Siredon), afford very good objects, owing to the large size of their sarcous elements. However, the same may be recognised in the smaller particles of the muscles of frogs, mammals, and human beings (4). The prisms appear noAv as cylindrical or hexagonal prismatic particles, of greater height than breadth. Their length in the proteus (fig. 278, 1, a) is 0.0017 mm., in the frog (fig. 280) 00013 mm., in the pig (fig. 278, 2, a) and in man 0*0011-0*0012 mm. Standing one beside the other, they form the dark transverse zones, and are almost in actual contact Avith one another as a rule, owing to the scanty amount of interposed cement (fig. 278, 2, a; fig. 279, a). Those spots are particularly instructive where the sarcous elements of a Fig. 1. Fig 2. Fig. 278.—Two muscle fibres from the proteus, 1, and fig. 2, magnified 1000 times. (The first was an alcohol preparation, the latter treated with acetic acid of roi percent.), a, sarcous elements; 6, clear longitudinal cement. At a, the sarcous elements are more separated from one another, and the transverse cement is visible. c, nucleus. Fig. 279.—Krause't transverse disks, a, a. 1, a muscle fibre without, 2, one under strong ex- tension ; both highly magni- fied (Martyn); 3, a fibre from the dog immediately after death. transverse row appear somewhat distant from one another ffio- 278 1 below, 2, a*). V °' In our description so far of the structure of the muscle fibre, Ave have intentionally followed up the historic course of the opinions held regarding it, in order to facilitate the comprehension of the most recent investi"a° tions by the reader. From the newest researches we learn that our earlier vieAvs were incom- plete. But still the field of inquiry is so exceedingly wide, the matters to be dealt with lie so near the verge of invisibleness, and the composition of the fleshy mass is so very .unstable, that the views of present-day observers differ widely. In the first place, the transparent transverse zone is traversed by a very fine dark line. This was referred to by the English observer Martyn with others, and the second edition of this hand-book, in the year 186*> TISSUES OF THE BODY. 289 Later on, its nature Avas made the subject of more extended research by Krause, so that we may name it the " transverse plate of the transparent zone" of Krause. This cross-line (fig. 279, a) may be recognised without great difficulty in the living muscles of mammals and the naked amphibia. It is to be seen very distinctly in the muscle fibres of insects, after pre- vious stretching, attaining a thickness at times of 0*0008 mm. After the action of A*ery Aveak acetic acid it is the source (at least very fre- quently) of the transversely striated marking of the muscle fibre of the vertebrates. Krause holds a very peculiar vieAv in r|spect to the structure of muscle (fig. 280). He regards the dark cross-line just mentioned as the optical expression of a delicate transverse parti- tion springing from the sarcolemma. Avhich divides the interior of the muscle fibre into a number of diskoid compart- ments built up one over the other. The contents of such a compartment, then, would consist from beloAv upwards of (I) half of a transparent transverse zone ; (2), of a dark zone occupying the middle (i.e., of a transverse disk of sar- cous elements); and (3), of another half of a transparent cross zone (see fig. 280). Krause believes also in the existence of a delicate lateral membrane, iiiA-est- ing closely the sides of the sarcous elements and ends of its transparent appendages, and uniting with the trans- verse membrane. In this Avay he sup- poses the elementary structures of the striped fibres to be formed—the so- called " muscle caskets." In longitudinal rows they constitute the fibrilla?. This author also believes the clear longitudinal and transverse cementing medium to be liquid, and that during contraction the layers of fluid flow from the end surfaces to the sides. Almost at the same time, however, Hensen observed the dark transverse zone to be divided in its middle by another transparent cross-line of Aveaker refracting power (fig. 281, a). This is noAv knoAvn by the name of the "middle-disk" of Hensen. The views regarding its nature are very various. By some (Krause, Heppner) it is regarded as an optical illusion, while others (Merkel, Engelmann) maintain its presence in the living fibre. The last vieAv, of course, does aAvay with the pre-existence of the sarcous elements. They would have to consist either of three portions,—two dark terminal, and a central transparent,—or could only be products of coagu- lation, assuming a homogeneous constitution after death, composed of the dark matter of the transverse zone and middle disk. Finally,minute granules have been remarked, arranged in roAvs, at each side of Krause's transverse lines These toavs have been named " accessory disks" (Engelmann) (fig. 282). Fig. 280.—" Muscle caskets," a; forming transverse disks at c lemma. *>, fibrilla r c, sarco- Fig. 281—Muscle-fibre of the lancelet {am- phioxus). a, the "middle disk" of Ilenten; b, transpa- rent transverse zone (alcohol prepara- tion). (Fidget, Merkel). 290 MANUAL OF HISTOLOGY. This does not appear to be the place for entering more deeply into the ^Thfstructure of striped muscle fibres will probably remain a matter of controversy for many years to come. We look, however, upon the cross-lines of Krause as fully substantiated. But as to the existence of lateral membranes, and the theory of the " muscle caskets" dependent on it, we do not believe in it any more than in the fluidity of the cementing medium. As regards the middle disks, Fig 282.-Portion of we have not vet come to any definite conclusion. We dead muscle fibre, i00k Up0n the sarcous elements as pre-existing in some uZ^7Z;b, form or other, and not as products of coagulation accessory disks. (Engelmann). In our opinion the longitudinal fibrillae are artificial productions. Unexpected results were obtained some years ago by a method of treat- ment practised by Cohnheim, namely, the preparation of transverse sections of frozen muscle. In these may be recognised groups P'lil^L 0I> sarcous elements, like a mosaic of small par- ticles of from three to six-sided figures. Between and bounding these is a trellis-work of transparent glit- ISk tering lines, which become broader only at irregular intervals. These belong to the transverse cementing medium. It is still a matter of uncertainty Avhether the ele- ments of unstriped muscle possess sarcous elements or not. lrM$W Briicke made a very interesting discovery long ago, V&W namely, that Bowman's sarcous elements, together Avith the cross-lines of Krause and middle disk, are Fig. 283.-Transverse double refracting, and are positively monaxial, whde section of a frozen °.» r : . . „ ,. frog's muscle, a, the cement deposited between them is single retracting. meTs'tTnucfeus6; The first are "anisotropic," the latter "isotropic." c clear cement. xhe correctness, however, of Briicke's statement has been since questioned by Rouget and Valentin. Remarks.—1. The slight inclination of the fibrillae to separate from one another (when no reagents are made use of) seems also to point to this conclusion. 2. " The muscle fibre is therefore just as little a bundle of fibrillae as a pillar built up of disks arranged one over the other. Should a total separation in both directions really take place, the result would necessarily be a breaking up into fleshy prisms." " And if we tear off a fibril from a muscle fibre we take away from every disk a sarcous element, and vice versa" (Bowman). 3. Dobie (Annal. of Nat. Hist., Feb. 1848) also discri- minated in the same manner long ago between the darker sarcous elements of Bow- man and a second system of clearer portions situated between them. Muscle fibres, when stretched, show, according to Martyn (Beale's Archives, Vol. iii. p. 227), another transverse line passing through the centre of each clear zone. The same was pre- viously observed by Amid, Koelliker, and others. I myself have remarked it frequently too. 4. They may assume very large proportions, also, in the crawfish. Here they were found by Hdkel to vary from 0*0020 to 00099 mm. in height; and he was able to isolate them in a gelatinous condition as long as 00114 mm. He looks upon them as hexagonal prisms. Amid's observations are also of great interest. According- to hiin, the elongated prismatic elements ot the muscle of the common house-fly, separated by a distinct cement or clear zone from one another, assume during contraction a marked obliquity of position. This I can corroborate myself. Farther, according to Schonn, there is a dark spot visible in each sarcous element. TISSUES OF THE BODY. 291 §166. The occurrence in its substance of certain foreign molecules, partly con- sisting of fat, is another peculiarity of the muscle fibre. These are known as the " interstitial granules of Koelliker," although described long ago by Henle. They are not ahvays distinct in human muscle, but when present are encountered in rows parallel to the direction of the fleshy fibres. In the muscle of the frog they appear with greater distinctness (tig. 284, d), and are often uncommonly numerous also, resisting, further, the Fig. 285.—Muscle fibre from the leg of a frog, after prolonged treatment witli dilute hydrochloric acid. From- the cut surface very fine fibres are seen projecting, a; with granules, 6; the latter are distributed along the whole fibre. action of water acidulated with hydrochloric acid entirely. Here they commence at the poles of the nuclei, and appear as though situated in a system of canal-like interstices, occupied by nuclei, granules, and fat molecules (Koelliker), which, under ordinary circumstances, are filled up with the well-knoAvn protoplasm. When coagulated, these masses may form a series of extremely delicate fibres (0*0006 mm. thick) and project from the cut end of a muscle fibre which has been treated with Avater contain- ing a trace of hydrochloric acid (fig. 285). The fibres contain fat mole- cules, partly externally, and partly in the interior. Ley dig, Bbttcher, and 0. Weber, erroneously regard these structures, together with the nuclei of the muscle, as a network of stellate connective-tissue cells with tubular pro- cesses traversing the substance of the muscle-fibres. On transverse sections of muscles which have been dried and subse- quently moistened (fig. 286, a), we see these rows of fat granules as a number of dark dots, as long as the molecules remain in the section, Fig. 284. 4 292 MANUAL OF HISTOLOGY. H if Fig. 286.—Transverse section of the hu- man biceps brachii. a, muscle fibres; 6, section of a large vessel; c, a fat-ceU in a considerate connective-tissue in- terstice ; d, section of a capillary vessel in the thin septum of connective-tissue between two muscle fibres; e, nuclei of the latter lying close to the sarcolemma. but as small round openings on their falling out »u^ bosides tt.e^ the sarcous elements appear, under low d magnifying poAver, more or less distinctly, in the form of extremely fine pale dots. §167. We now come to a special modifica- tion of striped muscular tissue, namely, that formed of branching or reticulated fibres. These are of frequent occurrence in the loAver animals, but are, as far as we know, at present confined to but limited portions of the human and mam- malian body. For many years past the occurrence of muscle fibres of this kind has been recog- nised in the tongue of the frog. Here they are seen dividing and subdiAuding at acute angles. In the same organ of man they have since been found by Biesiadecky and Herzig, as also by Rippmann, having been previously observed in some of the mammalia. In the lips and snouts ot many ot these animals the same variety of the tissue appears. On the other hand, the muscle of the human heart, and that of other vertebrates, shows -with the greatest fre- quency division of the fibres Avith anasto- moses; thus the formation of regular muscular networks. The muscle fibres of this organ (fig. 287) are smaller than elseAvhere, and richer likeAvise in fat molecules. Envelopes are less apparent than on other striped fibres, or are entirely absent. Finally, the trans- verse striae appear with greater distinct- ness, and the tendency to break up into fibrilias is here considerable. The union of adjoining fibres (a, b) is effected as a rule by short (c) and usually slender branches, which leave the stem noAv obliquely, uoav more transversely, so that a regular network is produced, very important in the mechanism of the motions of the heart. According to Koelliker's statements, each ramifying muscular element of the heart corresponds to a stellate cell, and the whole to a cellular netAvork. Weismann, however, declares that his investigations have led him to other conclusions. According to him, the muscle bands consist (and it is easy to convince ourselves of the fact), in fishes and amphibia, of simple elongated fusiform and sometimes branch- ing cells, associated together. The same is the case in the embryos of the higher vertebrates. In the latter, hoAvever, they become, later on, more closely united to But even here it is possible to Fig. 287.—Muscle fibres from the heart, after Schweigger-Seidel. To the right the boundaries of tlie cells and the nuclei are to be seen. JJ1 "■*■■"■ *o«"-ci, "uwovci, nicy uc^uiik form the common mass of the band. TISSUES OF THE BODY. 293 d Fig. 288. render visible the boundaries of the individual cells artificially (Aeby, Eberth, Schweigger-Seidel). In the other transversely striped muscles of the body it is the exception to find branching fibres. Kemarks.—The retiform connections of striped muscle fibres were described by Leuckart and myself many years ago, and probably for the first time, as occurring in arthropods, and noted later as of frequent occurrence among invertebrate animals. In the year 1849 they were again brought to light by Koelliker, having been pre- viously seen by Leeuwenhoek. § 168. The fibres of striped muscle are arranged parallel to one another (Avith exception of those of the heart), and appear prismatic, OAving to their mutual contact (fig. 288, a). Their direction is that of the long axis of the muscle. Be- tween them is situated a very small quan- tity of interstitial connective-tissue, in which the nutrient capillaries (d) and nerves of the part are contained. Several of these muscle fibres are usually united to form a bundle varying in thick- ness from 0*5 to 1 mm., and separated from the surrounding bundles by a stronger layer of connective-tissue. Such primary fasciculi are then combined to form secondary, which present themselves in very varying thickness. The connective-tissue envelope and uniting substance of muscle is knoAvn under the name of " perimysium," two kinds of which are recognised, namely, an external, enveloping the whole structure, the perimysium externum, and a continuation of the latter between the fibres, the perimysium internum. Fat-cells (c) may also be met Avith in the connec- tive-tissue of muscle, becoming more numerous in obese bodies, or in muscles Avhich have remained long unused. Seen from the side, they are ar- ranged in rows one after the other (fig. 289, b). They may eventually interfere Avith the ability of the fibres to perform their work. Bands of smooth muscle also, although they seldom form such bulky muscles in the human body as the first formation, are nevertheless put together in a similar manner in bundles, wherever they are crowded and collected in large numbers together. On the other hand, contractile fibre- cells appear frequently enough in the body iu very small aggregations, hidden and obscured by an excess of connective-tissue, so that they can only be discovered amid the latter Avith difficulty. Con- sequently, we may distinguish betAveen pure and mixed unstriped muscle (Koelliker). The A'ascularity of muscle is very considerable, and the arrangement of its vessels characteristic (fig. 290). The arterial stems entering the Fig. 289___Human mascle showing fat-cells, a, mus- cular fibre; b, rows of fat- cells. 294 MANUAL OF HISTOLOGY. muscle (a), send off to the fibrillae short transverse branches, which are then broken up into a delicate capdlary network (c, d), whose longitudinal tubes pa3s between the muscular fibres, and communicate with one an- other at long intervals by means of short cross twigs. Thus, a long-meshed capillary network is formed within which the muscle fibre is situated. The proper fleshy substance of the latter receives none of these capillaries. As to the venous vessels, their course corresponds precisely to that of the arterial. The nerves met with here will be considered in the next chapter. §169. As is well knoAvn, muscles are united very closely with their tendons, and in such a manner that the latter, in their course, appear to be either the immediate prolongation of the muscle fibres, or, the insertion of the latter into the substance of the ten- don takes place at an oblique angle. The arrangement of the tissues is, hoAvever, essen- tially alike in both cases. Yet for all this it was a long time before conclusive results could be arrived at here, owing to the want of suitable modes of manipulation. With a rectilinear insertion of the tendon, there appears to be no sharp boundary between the fleshy substance and that of the connective-tissue, so that a casual observer would be Avarranted in supposing an immediate transition of one tissue into the other (fig. 291). On the other hand, a completely different appearance is presented, where the insertion of the fleshy fibres is oblique, namely, a sudden termination of the latter, so that simple agglutination of tAvo tissues was supposed to exist here by Koelliker. Weismann, on the other hand, succeeded in demonstrating in every case, with the help of strong solutions of potash, the sharp termination of muscle fibres against the tendinous tissue. He shoAved them to be covered also here with sarcolemma (fig. 292, b), and to end rounded (a, b), pointed, or obliquely truncated, and so on. They are merely cemented to the tendinous bundle (c, d) at this point, although most securely. Other macerating fluids may be made use of with similar results, and even immersion in glycerine may produce the desired effect (Biesiadecky and Herzig). We are now met by the important question as to the length of the contractile fibres of muscles. Do they traverse the latter in their whole extent, or do they terminate before they have done so 1 It was formerly supposed that each muscle fibre was of the same length as the muscle to which it belonged. More recently, hoAvever, the interesting discovery Avas made by Rollett, that many of the fibres are not obliged to pass through the whole extent of the muscle in order to end in a tendinous bundle, but that the termination of the strongly pointed fibre Fig. 290.—Capillary net- work of a striped muscle. a, arterial vessel; 6, venous; c and d, the network of capillaries. TISSUES OF THE BODY. 295 may take place rather in the middle of the muscle (fig. 277, b). Continuous with its end, and playing the part of a tendon to a certain extent, we find interstitial connective-tissue. These statements were then subsequently corroborated by E. H. Weber, Biesiadecky, and Herzig, Aeby,. and Krause, who met with rounded and pointed forms of termination besides. Fig. 291. — Two muscle Fig. 292.—Two muscle fibres (a, b) after treat- fibres (a), with apparent ment with solution of potash. One of them is transition into the con- still connected with a tendinous bundle (c), nective-tissue bundles the other loosened from its attachment to of the tendon (b). one of the latter (d). We can also convince ourselves that the opposite end of the fibres may terminate in like manner. Krause is of opinion that no muscle fibre exceeds 4 c. m. in length, and that those which are apparently longer consist of two fusiform elements adhering together (?). Further investi- gation appears desirable here. In short muscles the fibres probably tra- verse, as a rule, the whole length of the muscle. In the longer muscles of the frog, also, we may convince ourselves that this does in reality take place (Koelliker, Weismann, Kiilme). Remarks.—The views Avhich were formerly most widely held may be arranged under two heads. According to the first of these, the fleshy mass was directly con- tinuous with the tendinous bundles; to the second, that the muscle fibre, terminating abruptly, was embraced externally at its end by the fibres of the tendon, in the same way that the finger of one hand may be grasped by the tips of those of the other. §170. In examining muscular tissue chemically, Ave should be able to separate its essential constituents, such as the striped fibres and con- tractile cells, from those which are mere accessories, namely, connective- tissue, vessels, and nerves. Further, we should be able to determine Avhat organic and Avhat inorganic substances enter into the composition of fibre and cell, and how they are distributed over nucleus, envelope, aud 20 296 MANUAL OF HISTOLOGY. contents. Finally, we should analyse the fluid saturating muscles, with its nutritive matters and products of decomposition resulting from the energetic transformative processes going on in the tissue. Zoochemistry, hoAA*ever, of the present day is unable to meet these requirements of physiology; and yet, muscle is one of those tissues which has received most attention to this end. In the year 1847, Liebig presented us with his elaborate treatise, and, more recently, Kiilme has essentially furthered our acquaintance with the subject by his elegant experiments on the muscles of frogs. From the already mentioned microchemical bearing, we gather that the substance of the sarcous elements, of the longitudinal and of the transverse cement, is to be recognised as three distinct materials with separate reactions. We have still, then, the nucleus, insoluble in acetic acid, dark transverse disk of Krause (also of resistent nature), and the sarco- lemma, with its reactions so similar to elastic tissue (but greater solubility in alkalies); so that, taken in all, there is very considerable complexity to be coped Avith. The specific gravity of striated muscle is stated to lie between T055 (C. Krause) and T041 (W. Krause and Fischer), while the proportion of water contained in it ranges from 78 to 72 per cent. (1). This water belongs first of all to the tissue of the fibres, then to the other structural con- stituents scattered among the latter, and finally, to the fluids with which the Avhole mass is saturated, the amount of which, however, is not yet known. This latter has been named the " muscle plasma." Like the plasmatic fluid of the blood, it loses, on the death of the muscle and con- sequent "spontaneous" coagulation as it is called, an albuminous substance, and becomes " muscle-serum " (Kiihne). The juice of living muscle has a distinctly alkaline reaction (Du Bois- Reymond); that of the dead tissue, or that affected by rigor mortis, is acid (Liebig). From the solid constituents of muscular tissue, which amount to some- Avhere about 20 per cent., Ave have first a varying quantity of glutinous matter to deduct, Avhich belongs to the commingled connective-tissue. About from 0*6 to 2 per cent, of glutin may be obtained from fresh muscle. The fresh tissue then contains, to the amount of 15-18 per cent., a series of albuminous matters, partly soluble and partly insoluble, with which Ave are still but imperfectly acquainted. These are in the first place con- stituents of the juices of the tissue, then again of the fleshy fibres of the latter. The soluble members of the group are for the most part remark- able for their coagulation at a low temperature (35-50° C-), a property which is to be met with only in those of the contractile substances of the system. Kiihne has obtained the spontaneously coagulating albuminous sub- stance of the plasma from the muscles of frogs, and has named it myosin (§ 12). It is the congelation of the latter which communicates to the , fibre of muscle its cloudy appearance on rigor mortis setting in. The coagulum. of myosin is insoluble in water, but soluble in solutions of common salt, which contain less than 10 per cent of CINa, likeAvise in dilute acids and alkalies. Three other albuminous substances, besides, may be obtained, according to the same observer, from muscle serum, namely, the so-called albuminate of potash, a second material, coagulating at 45° C, and a third, which requires 75° C, before the latter process takes place in it. TISSUES OF THE BODY. 297 If, on the other hand, muscle be treated with a very dilute solution of hydrochloric acid (1 :1000), another modification of the albuminate group is obtained, from the members of the latter contained in it, namely, syntonin. This body Avas formerly named " muscle fibrin," until Liebig prove its difference from fibrin. It may be obtained, moreover, by a similar process, from other albuminous matters, and is probably also formed physiologically by the action of the acid gastric juice during digestion. The quantity* of syntonin varies very much in the muscles of different animals (Liebig), and Ave are taught further, by the microscopic control of the fibre engaged in solution, that we have here to deal, not with a simple, but Avith a compound matter, consisting of three substances,—first, the longitudinal cementing medium, Avhich falls the first prey to the solvent action of hydrochloric acid, and then the sarcous elements and transverse cementing substance, Avhich are probably not simultaneous in their solution. Besides these, there remains over in the sarcolemma a slimy granular residue Avith fatty molecules. Neither nucleus nor sarcolemma yield any of this syntonin. The first affords no glutin (Scherer, Koelliker), but consists of a substance nearly allied to elastin, but differing from it in its smaller poAver of resistance to reagents ; the latter resists the action of dilute hydrochloric acid for days in the most determined manner (fig. 277, 5, a, b), but gives Avay on the other hand to strong alkaline solutions. Like all other tissues, muscle contains fat, but in most variable quantity. A certain proportion of it may be set down to the cells of the nerves and fat-cells of the fleshy mass, but a certain amount belongs to the fibres themselves. By means of washing and expression, about 6 per cent, of constituents, soluble in cold Avater, may be extracted from the dead muscles of the mammalia. They are of very various nature and great physiological interest. In the liquid so obtained, Avhich is of reddish colour, opaque, and of strongly acid reaction, Ave encounter, in the first place, a not incon- siderable proportion of soluble albuminoids, amounting in the fresh tissue to 2-3 per cent. We obtain in the first place, then, the red colouring matter of the muscular fibres in solution, which is identical with that of the blood (Kiihne), and Avith which the tissue is saturated during life. The tint of striped muscular tissue is more intense than that of unstriped fibres, and is, as a rule, only present, Avith any degree of markedness, among the higher vertebrates, whilst the flesh of the loAver members of this group appears in general but slightly reddened, or even quite pale. Besides this, the juice of muscle contains, as shoAvn by Liebig, a series of important products of decomposition, Avhich were knoAvn to earlier investigators as "extractives." Among these there appear, in the first place, several azotised substances. The first of these is kreatin (p. 44), whose amount is usually small, existing, it is generally supposed, in largest quantity in the heart. It varies also in different species of animals, and is more abundant in lean than in fat bodies, and likewise after muscular exertion. A hundred parts of fresh human muscle contain, according to Schlossberger, 0*06 of kreatin (in the horse. 0*07. according to Liebig), Avhile the heart yields 0*14 per cent. The next of the series is kreatinin (p. 45) (nearly allied to the last), Avhich appears to occur in smaller quantity than the last. Its occurrence, however, appears doubtfid 298 MANUAL OF HISTOLOGY. from Neubaur's investigations. Then Ave find hypoxanthin (p. 43). Strecker states the amount of the last of these to be only 0*022 per cent, in the fresh flesh of oxen. In addition to these, a fourth substance, xanthin (p. 43) is supposed by Scherer and Staedeler to exist in the flesh of mammals. A new substance, discovered by Weidel in Liebig's extract, may also be mentioned here, to which the name of carnin has been given. Urea is not usually present in human muscle ; tyrosin and leucin are also absent (2). The muscles of embryonic pigs of two inches long, however, contain, besides kreatin, a moderate amount of leucin. In muscular tissue also there is a peculiar species of spurious sugar, which has been named inosite (p. 33), and which has up to the present only been met with in the substance of the heart. According to Valen- tiner, it appears to be a normal constituent of the muscles of drunkards (3). Staedeler met with it also in the muscles of dogs. Meissner has likewise demonstrated the presence of a kind of sugar, " muscle sugar," peculiar to muscle, in the flesh of the five classes of vertebrata, although as yet no one has succeeded in obtaining it in a pure state. It is a matter of some interest, further, that the embryonic muscle fibre, as well as the contractile fibre-cell, both contain glycogen (Rouget, Bernard, and Kuhne); but it appears also to be regularly present at a later period (0. Nasse). In that the muscles of phytophagous mammals contain dextrin, the occurrence of this muscle sugar is easily explained. The series of organic acids is no less considerable. In the first place, we have 0*6-0*7 per cent, of paralactic acid (p. 34)—the source, apparently, of the acid reaction of dead muscle. It Avas formerly supposed with Liebig that it was a component of every living muscle also, but Du Bois- Reymond showed later that the plasma of quiescent or moderately active muscle has a neutral or Aveakly alkaline reaction, and only becomes acid Avhen the structure has been called on for immoderate exertion. On the other hand, after the death of the muscle, which is ushered in by rigor mortis, the fluid of its parenchyma becomes rapidly acid by virtue of the presence of free lactic acid. As to the particular constituent of the muscle from which this acid has its origin, we are at present unable to answer anything with certainty. Besides this, Ave meet Avith inosinic acid (p. 36), according to Liebig, about which but little is knoAvn, and which appears also in very small quantity. Schlossberger, however, was unable to discover it in human flesh. Further, muscle juice contains of the volatile fatty acid group butyric, acetic, and formic acids. Uric acid was only once met Avith by Liebig. Finally, the mineral constituents of muscle (of the tissue as Avell as con- tained fluid) are very peculiar. The same compounds as those occurring in the plasma of blood are certainly met Avith, but in completely different proportions. While in the latter the combinations of soda preponderate, muscle tissue sIioavs the greatest poverty in soda, and an excess of potash. In contrast also to the plasma of blood, the phosphatic salts exceed in muscle the combinations of chlorine by a large amount, the greater part of the phosphoric acid being united with potash, and the proportion of chloride of sodium appearing but very inconsiderable. In conclusion, among the combinations of phosphoric acid Avith earths, we find the raagnesian phosphate exceeding in amount the corresponding salt of calcium. Iron is also contained in flesh in a small quantity. The absence of sulphates is rather remarkable. TISSUES OF THE BODY. 299 When the question is started, Where are we to suppose these mineral constituents to exist, whether in the fibre or its nutritive fluid 1 the fol- loAving fact may be borne in mind, that the proportion of salts soluble in water which are present in flesh is very considerable. The former amount, according to Chevreul, to 81, and to Keller, to 82*2 per cent of the whole ash, while the quantity of phosphate of calcium is stated to be 5*77, and that of magnesian phosphate 12*23 per cent. Of course a larger proportion of potash compounds must occur in the fluid of muscle than in the fibre itself, whereas the latter is richer in phosphatic earths. Living muscle contains, further, carbonic acid and oxygen gases. The latter is absorbed by it so long as its vitality exists, Avhile carbonic acid is generated within it as a product of decomposition, Avhether blood be conveyed through it or no. The amount, moreover, of the latter increases with the use of the muscle, Avhich appears to be one of the most import- ant sources of this ultimate product of mutation in the body. Smooth muscles, with the contractile substance of their cell body and their nuclei, manifest less complication than those formed of striated fibres, but appear on account of their smaller bulk less suitable objects for chemical investigation. Their composition appears, moreover, to be the same as that of the striped tissue. Syntonin has naturally been obtained from them also (Lehmann). Further, in their juices albuminous substances have been found—kreatin, hypoxanthin, lactic, acetic, formic, and butyric acids. Here also the potash combinations predominate. Remarks.—1. Bibra states the proportion of water in the human muscle to be only 72-74 percent., as opposed to the usual figures, 77-78. 2. Among the fishes we find the muscular tissue of the plagiostoma to contain enormous quantities of urea (Staedeler and Frerichs in Erdvmnn's Journal, Bd. 73, p. 4i>, and Bd. 76. p. 58). 3. The same observers found, further, a substance very similar to inosite in the muscles of the plagiostoma ; this is named "scyllit." §171. In regard to the many physiological and physical properties of the tissue, a few points only need be touched on here. Quiescent living muscle displays a high degree of extensibility, return- ing almost completely to its original length as soon as the extending force is suspended; it has slight, but very perfect elasticity. The active fibre is still more extensible, i.e., its elasticity has undergone diminution. The dead muscle fibre possesses much less capability for being extended, and return to its original length does not take place. The living structure possesses electromotor properties, and presents the so-called "muscular stream," in the study of which Du Bois- Reymond has lately done so much. We cannot here enter upon its differences during quiescence and activity of the muscle. The latter ceases to possess electromotor properties so soon as its vitality is at an end. The most important property, however, of the living muscle fibre (striped and smooth) is, that it contracts on stimulation of the motor nerves terminating in it, decreasing in length, and enlarging it in a trans- verse direction. The nature of this peculiar property inherent in muscle— whether it be itself capable of being excited, or only through the medium of the nerves Avhich end in it—has been now for many years the subject of physiological controversy. 300 MANUAL OF HISTOLOGY. The kind of contraction, again, varies according to the histological elements with Avhich Ave are engaged. In striped fibres Ave observed it to commence almost simultaneously with the application of the excitant to the nerves of the part, ceasing very rapidly again on cessation of the stimulus, and giving Avay to relaxation. The reverse may be observed in smooth muscle. Here an appreciable interval of time is remarked be- tween the application of the stimulus and contraction, Avhde the latter outlasts the action of the excitant for some moments; tho fibre reassum- ing gradually a condition of quiescence. This is evident in the motions of°Avhole groups of animals, and also in those of individual organs, as in the iris of birds, made up of striped fibres in contrast to that of human beings and mammals generally, in Avhich the former are smooth. With us it is the striated fibres alone which obey the influence of the will in their rapid and precise action. In the rectdinear muscle, Avith the aid of the microscope, Ave see during contraction the longitudinal striae become less distinct, and eventually disappearing, while the transverse markings become clearer and clearer. It would naturally be a great point achieved could Ave ascertain precisely how the elementary particles of the active fibre are affected by this, and especially how the dark zones behave in relation to the clear. It appears, hoAvever, as though the former approached each other, Avhile the clear zones decreased in height. These points are, however, still too doubtful for us to be able to draw any great conclusions from them. We regard it as not improbable, hoAvever, that the sarcous elements may be relatively immut- able, as compared with the particularly contractile longitudinal cement- ing medium. According to Amici's observations on the muscles of the common fly, the elongated fleshy particles appear to assume an oblique position at the moment of contraction. This we have ourselves seen. According to the most recent observer, W. Engelmann, the seat of the contracting force is exclusively the dark (anisotropic) layer. The trans- parent (isotropic) transverse zone is either contractile in a minor degree, or only elastic probably, like the dark transverse disk of Krause. Whde the volume of the muscle casket enclosed between tAvo of the latter does not become appreciably lessened, the dark transverse zone at the moment of contraction increases in bulk, the clear becomes less voluminous; the first swells, the last shrinks, so that an overfloAV of fluid takes place. Besides this the first becomes clearer and softer, the latter darker and more solid. ■ The sarcolemma, owing to its elasticity, follows the changes of form in the fibre, tightly investing the latter throughout. That the transverse stria*} are not produced by Avrinkles across its substance was recognised long ago. The motor nerves will be referred to in a future chapter. It is a matter of far greater difficulty to obtain a view of the contractile fibre-cell, or unstriped fibre, in the moment of contraction. According to Heidenhain, each element (at least among invertebrate animals) be- comes likewise simultaneously and evenly thicker in all its parts, Avith a corresponding decrease in length. As to the rigor mortis connected with the death of muscle, on Avhich an albuminous substance contained in the latter undergoes coagulation, Avhile its reaction becomes acid, the microscope has added but little to our knowledge. Tho dead fibre appears more rigid and dull, and less transparent than during life. TISSUES OF THE BODY. 301 §172. Turning uoav to the development ofthe tissue, we find smooth muscle to take its rise from the simple transformation of round formatiAre cells Avith spheroidal vesicular nuclei of the middle germinal plate. These elements change into contractile fibre-cells by groAvth in tAvo opposite directions, during Avhich the nucleus assumes its before-mentioned elongated con- figuration (p. 281). Fig. 273 (a, b) represents two such embryonic cells from the Avail of the stomach of a fcetal pig two inches lono-. Touching uoav the striated structures, it Avas for a long time supposed, in accordance Avith Schwann's view, that the fibre Avas always produced by a fusion of formative cells arranged in rows, Avhose united membranes Avent to form the sarcolemma, Avhile the nuclei persisted, and the com- bined contents of the cells took on the characteristic form of fleshy matter through further metamorphosis. But this view is, as Ave noAv know for certain, quite erroneous. The muscular fibre, far from being a result of the fusion of a series of cells, is nothing more than a single elongated filiform cell, in Avhich the nucleus has undergone division and multiplication, and the contents metamor- phosis, and which has attained gigantic dimensions in proportion to the length of the striped muscle. We have already referred to this mode of development (for the discovery of which Ave are indebted to Lcbert and Remak) in discussing the growth of the tadpole (p. 96). In the mammalia and human beings the same is to be observed. Here Ave may follow up, in young embryos, the steps in development of the tissue, which are essentially similar. Thus in the human foetus, at about the sixth or eighth week, very narrow membraneless and fusiform cells, often only 0*0025-0*0036 mm. in breadth, are met Avith as elements of the rudimentary muscle of the hands and feet. They* are formed of very delicate protoplasm, Avith a single or double vesicular nucleus, and attain a length of 0*14-0*18 mm. (Koelliker, Frey). The same is to he seen in mammalian embryos at corresponding stages of development. In those of the sheep, measuring 27-9 mm. in length (fig. 293), Ave may obtain from the diaphragm and abdominal muscles fusiform cells 0*28-0*38 mm. long, and 0*0045-0*068 mm. in breadth. These shoAv a vesicular nucleus 0*0077-0*0101 mm. in diameter, and incipient transverse striation in the central portion (a, b). These nuclei range in number from two to four, but other cells further advanced possess many more ofthe latter (c), and increase in transverse diameter to double or even more (d). As a rule, their axis remains unaffected by the transverse striation, and in it Ave see the original protoplasm. In some- what older animals the muscular fibre is 0*0129-0*0156 mm. in thickness, and so long that it can no longer be isolated in its entire length, although the pointing of one end (e). or blunt rounding off of the same (/), may be easily found. The number of nuclei now becomes greater and greater, and the process of division is observed as an ordinary occurrence (e>/> #)• Sometimes the position of the former is central (/, g, i) and sometimes peripheral (//). The axis of the fibre generally remains free from transverse marking (/, h, g), Avhile at its circumference the longitu- dinal cleavage commences to manifest itself. The tendency among muscles of this kind to break up into thick discs under the action of water (?') is a point of much interest. 302 MANUAL OF HISTOLOGY. Foetal muscle, as already remarked, contains glycogen, but at first, before the embryonic cells have begun to undergo their characteristic transfor- mation into fibres, this substance is entirely absent, according to the interesting investigations of Ber- nard and Kiihne. In smooth nucleated fibres it presents itself as a granular matter deposited around the nucleus. Rouget, how- ever, asserts that it only occurs diffusely. Later on, with the de- velopment of the transverse striae and appearance of the characteristic muscular structure, the fibre is in- filtrated with glycogen, which per- sists until birth, disappearing rapidly on the commencement of respiration. As yet we have not said one word as to the origin of the structure- less envelope, the sarcolemma. In earlier years, supposing the for- mative cell to be endowed with an envelope, this sarcolemma was looked upon very generally, as be- ing the metamorphosed cell-mem- brane of the former. But now that we have convinced ourselves that no such envelope exists upon the formative cell, such a view can no longer be entertained. At the present we find two theories Arery generally held in regard to this point. According to one, the sar- colemma is a hardened secretion from the cell, of the same nature as the so-called cuticular forma- tions ; according to the other (and we are inclined to favour this vieAv) this structureless sheath is a connective-tissue formation laid down on the muscle fibre from Avithout, which may be compared to the elastic bounding layers of _,. . j . , many connective-tissue structures. lhat the end of the muscle fibre can be separated with its envelope from the tendon, as we have seen at p. 294, appears to us to be no very weighty objection to this view. Do we not also see elastic fibres sepa- rating themselves from connective-tissue bundles? and yet they have both the same origin. The branching muscular elements of the heart correspond, we are assured by Koelliker, each to a metamorphosed stellate cell, and the whole to a cellular network. Weismann, however, is opposed to this theory from his own observations. In his opinion the muscular bands consist (and of Fi«C 29:).—Development of striped muscle fibres: from a fetal sheep, a, b, very long fusiform ceils with two or three nuclei and commencing stria- tion ; c, d, portion of a somewhat more mature fihre, with numerous nuclei and considerable dia- meter; «,/, g, fibres still further developed, with nuclei in the axis; h. nuclei beneath the enve- lope ; t, a fibre breaking up into thick discs. TISSUES OF THE BODY. 303 this we may convince ourselves very easily), in fishes and amphibia, of aggregations of simple elongated fusiform and at times branching cells. The same is the case in the embryos of the higher vertebrates. In the latter, however, these cells unite more intimately at a subsequent period to form the common substance of the band. But we may still render the boundaries of the various ceUs visible here also by artificial means (Eberth). §173. Let us noAv turn to the growth of muscle. Embryonic muscular fibres, as we have already mentioned in the previous section, are considerably finer than those of the infant, and their diameter in the latter is far less than in the adult. According to Harting's accurate measurements, the muscle fibres of the adult appear about five times as thick as at the time of birth. This increase in length and breadth is brought about by the reception of new particles between those already present in the fleshy substance, or, as it is the custom to say, by intussusception. But the fibres of growing muscle become not only larger, but their number also increases, as Avas demonstrated beyond gainsaying by Budge, by experiments on the sural muscles of a frog's leg. We are indebted to Weismann also for further interesting information on the same point. According to the last-named observer, the growth of the muscles of frogs takes place only in part through increase in thickness of the fibres originally present; there occurs, besides, a considerable augmen- tation of the number of the latter by a process of longitudinal division. This process is ushered in by an active proliferation of the nuclei or muscle corpuscles (Muskelkbrperchen) in the old fibre, so that we soon meet with regular columns of the former arranged one over the other, whde the fibre itself becomes flattened and widened. Subsequently to this the fibre splits into two threads, in each of which the process just described is repeated, so that out of one old muscle element a whole group of new ones eventually takes its rise. Each of the new fibres then attains its typical diameter through that growth from within, which has already been referred to. In full-grown frogs, also, during their Avinter torpidity, Ave may see a lively regeneration, with fatty degeneration of the previously existing muscle fibres (Wittich). In this case, likewise, the same process of multi- plication was observed by Weismann. Great interest attaches further to a discovery made by Lenker, that an extensive destruction of human muscle fibres takes place during typhus fever, combined with rapid multiplication of the muscle corpuscles and connective-tissue cells. This is due to a peculiar degeneration, and is fol- lowed by energetic regeneration of the elements on recovery. The pro- cess is probably the same as that observed in the hibernating frog. This luxuriant growth of the muscle corpuscles takes place, besides, in other states of irritation of the tissue. From these facts, feAV though they be, we may infer that muscle fibres are by no means so persistent structures as was formerly tacitly agreed to. The uterus of pregnant women offers us a good opportunity of setting on foot interesting investigations as to the nature of the growth of the elements of unstriped muscle. As is Avell knoAvn, the organ in question 304 MANUAL OF HISTOLOGY. Fig. 294. — Human muscle studded with fat-cells, a, muscular fibre; b, rows of fat-cells. increases enormously in volume at certain times, a fact Avhich depends chiefly on changes in its muscular tissue. The contractile fibre-cells become enlarged to 7-11 times their original length, and to 2-5 of their breadth (Koelliker). Besides this, there takes place, according to the same observer, a reproduction of cells also. After parturition a decrease in the size of the contractile cell begins to be apparent, with which it returns in about three weeks to its original dimensions. Fatty infiltra- tion of the substance of the latter during this period is of frequent occurrence, and we may also accept as a certainty the resolution of a certain number of the muscular elements also. That there really may be such a thing as a phy- siological hypertrophy of the striped fibres can hardly be doubted any longer since Auerbach's dis- coveries. In hypertrophied hearts it Avas stated by Hepp long ago that thickening up to four times their original size took place in the fibres. It Avould appear, hoAvever, that there is really only a multi- plication of the fibres here (perhaps by longitudinal division). Pathological hypertrophies, however, of un- striped muscle, amounting even to the formation of tumours, are of frequent occurrence. They affect parts which are richly supplied with this tissue, such as the oesophagus, stomach, and uterus. Their genesis requires to be made the subject of more accurate investigation than has as yet been the case. That a transformation of connective-tissue cells into contractile elements takes place is at least probable (Aeby, Arnold, Koelliker). Finally, Ave meet with an atrophy of muscle fibres or disappearance of the same. In the first place, this is encountered as a more or less normal pheno- menon in old age. Then, again, it appears more fre- quently under pathological conditions as a diminu- tion in the diameter of the fibre (as in paralysis of various members), combined, to a certain extent, with fatty degeneration of the fibre or development of in- terstitial fat-cells. The latter (fig. 294) have been already discussed (§§ 122 and 169). If this latter pro- cess proceed to too great length, it may possibly inter- fere at last with the functions of certain portions of muscle through pressure, as, for instance, in the heart. The deposit of small molecules of fat in the interior of fibres is of frequent and normal occurrence Avhen the quantity of the former does not become too great. Thus Ave meet with it in the muscle of the heart, and in the frog in the muscles of the extremities (§ 166). In a greater degree it must be looked upon as a pheno- menon of retrograde development (fig. 295), of patho- logical significance. But, on carefully searching through healthy muscles, we will always encounter certain fibres containing a considerable amount of fat granules of this kind, and not unfrequently also a diminution in thickness, so that it is Fig. 295. —Fatty de- generation of human muscle fibres, a, low degree; b, a higher; c* the highest degree. TISSUES OF THE BODY. 305 probable that a physiological decay with fatty degeneration also takes place to a limited extent. Calcification of this tissue is rarely seen. Xeoplasis of striped muscle, at points where it did not previously exist is of very unfrequent occurrence. A certain number of those feAV cases which have been up to the present recorded have reference, strange to say, to the testicle and ovary. Here there can hardly be any doubt of the development of muscle fibres from connective-tissue cells, however we may suppose their source to be from the muscle corpuscles in the intra- muscular new formation. Though it was formerly believed that Avounds of muscles could be repaired by connective-tissue alone, numerous recent observations have proved the poAver of regeneration inherent in the tissue. The mode of this new formation of muscle is a matter, hoAvever, about Avhich much difference of opinion still exists. E. Composite Tissues. 15. Nerve Tissue. §174. The form-elements of the nervous system (1) are structures of two different kinds, namely fibres and cells, imbedded in a ground-work of con- nective-tissue. The first of these, knoAvn under the several names of '■' nerve fibres," "nerve tubes," and " primitive fibres " of the nervcfus system, make up almost exclusively the Avhite substance of the neural apparatus. The last, to which the names of " nerve or ganglion cells " have been given [also " ganglion corpuscles" (" Ganglienkorper ")], are found mixed up with the first described elements, in the grey matter. The "groundwork" of connective-tissue pre- sents itself in the first place in the form of a highly developed fibrillated structure, more fre- quently, hoAvever, as a more or less homogeneous connecting substance (perineurium), or, finally, as an extremely delicate tissue containing cells and nuclei, as in the nervous centres. Nerve-fibres (tig. 296) are met Avith either as dark-bordered threads, the medullated, or pale, the non-medullated. They are simple un- branched fibrils, except at their origin and termination, and vary to an extraordinary extent in thickness, measuring from 00225 down to 0*0018 mm. and less. Owing to their appear- ance not being the same in all cases, we dis- tinguish between broad or coarse fibres (a and b) of 0 02 J mm. (more usually of 0*0113-0.0056 mm.), and .fine or narrow fibres, whose diametu may fall to 00045-0 0018 mm. (c, d, e). Dark-edged nerve fibres consist of three parts,-namely, of a verydeli- cate envelope of connective-tissue, the "neurilemma « P«tive sheath;" of an albuminous portion extending down the centie, the so Fig. 296.—Nerve fibres from the human being, a, a coarse speci- men ; b, medium-sized fibre; c, d, e, finer still. 306 MANUAL OF HISTOLOGY. called "axis cylinder;" and of another portion situated between the envelope and the latter, a mixture of albuminous substances, cerebral matters, and (?) fats, the "medullary sheath" or neural medulla" (Nervenmark). Of these three, Avhich cannot be demonstrated on the perfectly fresh fibre, but only by round-about modes of treatment, the axis cylinder must be looked upon as the most essential and only indis- pensable structural constituent. The appearance of broad nerve fibres in a recent state is that of threads formed of some completely homo- geneous transparent or milky mass. It is rare, however, that we obtain a view of them in this state, owing to the exceedingly rapid changes which take place in the contained matter. All the more customary modes of preparation (if we desire to isolate the fibres) bring the latter before us in a form Avhich has already under- gone change, or has " coagulated," as the saying is. This congelation, however, is met with in various stages of completeness (fig. 296, a, b; fig. 297). When isolated Avith as great rapidity and care as- possible, the nerve fibre presents to our view a dark border, and closely applied to this internally a second and finer bounding line (fig. 296, a, b; fig. 297, b, above). Later on, these tAvo lines or "double contours" are not quite par- allel, and the internal one is no longer continuous throughout. The thin layer interposed betAveen the two lines on each side of the fibre appears homogeneous (fig. 2 9 6, a, b) or granular. At this stage of transformation the nervous fibre may remain stationary, the outer coagulated layer acting to a certain extent as a protecting covering for the portion situated more internally, or, the congelation may advance further at points, and the nerve fibre may frequently present a com- pletely different appearance at various parts of its course (fig. 297, 6). After this the internal line becomes separated more and more from the outer one, while between the two, and also in the central part of the fibre, lumpy, granular, or globular masses are formed (a, b), until eventually the Avhole appears transformed into a sometimes coarse and sometimes finely granular substance (c), and the entire nerve tube has become dark (2). Kemarks.—1..Literature is very rich in information on this subject. 2 Neural P^X^SVSS^^ from its sheath displays precisely t}'e same chaD*es §175. The existence of an envelope on the nervous tube is easily inferred Fig. 297.—Human nerve fibres at an advanced stage of coagulation. TISSUES OF THE BODY. 3Q7 from the fact that the latter can be isolated in a considerable part of its length, in spite of the soft nature of its contents. This neurilemma may , be seen not unfrequently as a short empty tube, at points where the included mass has been displaced (fig. 297, c). It may likewise be demonstrated by means of chemical reagents, which completely or par- tially dissolve the substance contained Avithin it (fig. 298, a, c). Neurilemma consists either of elastin or some material nearly allied to it, and is usually encountered among the higher vertebrates and in the human body as a completely homogeneous and very delicate membrane, either with or Avithout nuclei. Among the loAver orders of vertebrates, and on the peripheral ramifications of human nerves, it may be found thickened and supplied with numerous nuclei. To what extent this sheath exists among the elements of the nervous system is a more difficult question, and one which cannot at present be answered Avith certainty. Thus, in the branches of many of the cranial nerves it is absent; and in the terminal peripheral ramifications not unfrequently. Its demonstration, moreover, on very fine medullated nervous tubes is a matter attended Avith some dif- ficulty. Finally, the fibres ofthe brain and spinal cord are destitute of this sheath. The axis cylinder of Purkinje, or ■primitive band of Remak, cannot be recognised in the fresh nervous tube on account of its delicacy and soft consist- ence. It is frequently missed also in many simply coagulated fibres, owing to the fact that it also has undergone a granular metamorphosis. It appears, howeArer (and upon this Ave would lay greatest stress), at the point of origin (fig. 298, g), as well as at the terminations of the nerve tubes, Avhere the medullary sheath fails. It is likewise to be seen in many nerve fibres, coagula- ting in the ordinary manner, as a pale homogeneous band-like structure, about a fourth or third of the breadth of the former, projecting from its cut end (fig. 297, a, above). Certain chemical reagents again may be employed for its demonstration to great purpose. Among these are several sub- stances, in the first place, which are well known to render the protein bodies hard, Avithout dissolving or producing any particular effect on the fats; these are, for instance, chromic acid, chromate of potash, and chloride of mercury (fig. 298, 6). Again, there are reagents which are employed for the same ends on account of their poAver of disscdving the fats, but not the albuminates ; of these we may mention alcohol and boiling ether (a). Sometimes Ave obtain specimens in which the axis cylinder projects from the cut end " like the wick from a candle." One of the best aids, hoAvever, Fig. 298.—Nervous fibres of various kinds. a, a broader one from the frog after treatment with absolute alcohol, show. ing the axis cylinder and neurilemma; 6, another, witli axis cylinder, after treat- ment with bichromate of potash; c, a fibre from the same animal, treated with collodium, showing the axis cylinder and neurilemma; d, a non-medullated fibre from the petromyzon with the axis cylinder and nucleated envelope; e, a non-medullated fibre from theoUactory of the calf; / g, h, fine fibres from the human brain with axis cylinders; the fibre d (copied from R. Wagner) unites above with the process of a ganglion cell. 308 MANUAL OF HISTOLOGY. in the demonstration of the structure in question, is collodium, recom- mended by Pfliiger. Under its action the axis cylinder makes its appear- ance almost instantaneously throughout the whole length of every fibre, fre- quently bent over strongly to one side (c). Tinction with carmine may also be employed, and aniline (Frey) or chloroform ( Waldeyer). Very instructive objects, as regards the nature of the structure just described, may be prepared from transverse sections of nervous trunks previously artificially hardened (Reissner). In these Ave recognise the envelope of each tube, its axis cylinder as a small central formation, and between the two the medullary sheath. In the latter may be seen an irregular concentric marking, first observed by Lister and Turner, Avhich is probably the optical expression of lamination in the medullary substance. Transverse sections also, through the white substance of the spinal cord, present the same views of the axis cylinder, and medullary matter. Remark.—Quart. Journ. of Microsc. Science, 1860, p. 29, pi. 2. §176. Turning now to the ./me dark-edged nerve fibres (fig. 296, c, d, e), we find it possible here also to demonstrate in many cases the presence of the primitive sheath, although with greater difficulty. We recognise at the same time the axis cylinder, especially in the fibres of the brain and spinal cord (fig. 298,/, g, h), Avhere the primitive sheath is no longer present. It is a striking fact that, in these fine nervous tubes, we do not remark the same inclination to lumpy or granular coagulation as is seen to such an extent in the broader ones; Ave find them rather preserving theii transparency, whether their contour appear double, as in larger speci- mens (fig. 298,/), or single, as in the more minute (fig. 296, c, d, e). In a degree proportionate to their thinness, these fine nerve tubes are remarkable for being subject to a displacement, and the formation into globules of their medullary substance under the action of water, or from pressure, tAvisting, &c, in consequence of Avhich they often present a knotted appearance (fig. 296, c, d, e, and 298, h). These swellings are known as "varicosities," and are nothing, we repeat it, hut artificial productions, Avhich do not exist in the living body. Next in succession to these dark-edged medullated fibres, Ave come uoav to a second species, namely, to the pale er non-medullated. This is the primary form of all the fibrous neural elements in the embryos of man and the vertebrates. In the family of the petromyzon, a loAvly organised fish, this non- medullated pale appearance of the fibre, presenting simply an axis cylinder, persists throughout life (tig. 298, d). But even in the bodies of the higher vertebrates, and human beings also, the nerve tubes may still preserve this original embryonic condition in various positions; thus, in the nervus olfactorius, as soon as it enters the nose. While there can be but little doubt as regards the nature of the fibre-elements in the olfactory nerves, it is quite a different matter in the course and distribution of the sympathetic. Here Ave encounter in the human body and among the higher vertebrates, together with medul- lated tubes, the so-called fibres of Remak (ganglionic nerve fibres), which may even preponderate. These are transparent sometimes ; flat bands of about 0*0038-0*0068 mm. in breadth and 0*0018 mm. in thickness (fig. 299, 300, b). Their appearance is usually homogeneous, Avhile at intervaTs TISSUES OF THE BODY. 309 an elongated oval or fusiform nucleus may be remarked, measuring about 0*0068-0*0113 mm. in length. At times, also, these flat fibres are split up, though imperfectly, into fibrilla; (fig. 299, b). As to the nature of these fibres of Remak, Avhether they are composed of connective-tissue, or are (as Avas supposed by their discoverer, and with him by J. Muller) nervous elements, are points which, in the annals of histology, have been the subjects of controversy for years past. The existence of similar pale nerve elements among the lower animals and in the petromyzon, and among the embryonic and olfactory fibres of the higher animals, seems to point to the conclusion that they are of nervous nature, and, indeed, the general opinion grows stronger from year to year that this is the case. They are just nerve-fibres destitute of medullary sheath, and in which the axis cylinder is enclosed Avithin a nucleated Fig. 300. — A small nervous branch from the sympathetic of a mammal. Two dark- bordered nerve tubes, a, among a number of Remak's fibres, b. neurilemma. On the other hand, it must be granted that young imma- ture connective-tissue may present precisely the same appearance. The nucleated envelope of many ganglion cells is also a difficult point for us, which will be discussed in the next chapter. In some small trunks of the sympathetic system (fig. 300), the propor- tion of these pale fibres (b) is so large, and the number of the medullated tubes is so small, that it is difficult to conceive what would be the object of such an enormous amount of enveloping connective-tissue for so feAv nervous fibres. In the nerves of the spleen of fully developed mammals twigs have been found of 0*45 mm. in thickness, Avhich contain nothing but Remak's fibres. The question whether this variety in the appearance of the nerve-fibres corresponds to a difference in their functions or energies must be generally negatived. The nerves of voluntary muscle and those of the skin have, for instance, the same kind of fibres. The preponderance, hoAvever, of narrow dark tubes in the sympathetic is certainly remarkable, but the same occur in great abundance in the brain and spinal cord. Transitions from broad to narrow fibres are also numerous, and in the sympathetic Fig. 299.—Remak's fibres from the calf or, simple flat nucleated bands; 6, a fibre split above into fibiilte. 310 MANUAL OF HISTOLOGY. Wt I I system as Avell as in the olfactory nerves, as has just been mentioned, pale, non-medullated, nucleated fibres are to be found. But our position is far more difficult when we are asked for an ansAver to the question, whether, hi Avhat has been just described as the texture of the nerve tubes, their whole structure has been given, or Avhether they possess a further and more complex constitution. For many years past there has been no lack of efforts (and some very daring) to prove the latter to be the case. Only one point, however, of any great importance has been ascertained, through the im- proved optical auxiliaries to our investigations, namely, that the axis cylinder is made up of ex- tremely delicate fibrillar, imbedded in a finely granular substance. This fact was first recognised in the pale nervous tubes of many invertebrate animals, and in the olfactory nerve and fibres of Remak of the vertebrates. It is also true for the axis cylinders of the nervous centres (fig. 301), according to Schultze. These extremely fine fibres, on Avhich delicate vari- cosities may be remarked after treatment with certain reagents, have been named " axis fibrillar" by Wal- deyer, and by Schultze " primitive fibrillae." The axis cylinders of the stronger nerve tubes ap- pearing thus as bundles of the most delicate fibres of immeasurable fineness, those of less diameter must be looked on as collections of smaller members of the same, until eventually, in the most minute axis cylinders, the number is reduced to one single pri- mitive fibril (1). Later on we shall see that the primitive fibrilla (which call, however, for closer observation as to their nature) make their appearance naked, and separated one from the other in the termination of numerous fibres, and also constitute important fibrous elements in the nervous centres. Remarks.—1. The importance ofthe facts but briefly mentioned in the text entitles them to more extended consideration. It was Remak Avho first pointed out, years ago, this remarkable complication in regard to the axis cylinder of the craw-fish. In the gangliated cord of the latter are to be found, besides others, unusually thick nerve fibres, wbose axis cylinders consist of bundles of above a hundred of the finest fibrillae, only 0 0004 mm. in diameter. This was subsequently corroborated by Hdkel, Leydig, C. Walter, and Waldeyer, with discoveries of similar composition in the nerves of other invertebrate animals. M. Schultze observed the same structure in the axis cylinders of the olfactorius and nervous centres of vertebrates. As to the further points of interest in regard to the structure of the nervous tubes, we have already referred (p. 308) to the concentric markings to be seen in the medullary substance on transverse section of the latter. It seems to depend on lamination, but this view has been opposed by Frommann. According to Klcbs, the axis cylinder is imme- diately surrounded by a fluid substance,—the " periaxial fluid." Years ago Stillinq also described as very complicated, the structure of the nerve fibre, workino- with very high microscopic powers, and preparations made in chromic acid. Compare Lockhart Clarke in the Quart. Journ. of Microsc. Sdence, 1860, p. 165. More recently still Frommann and Grandry have described a transverse striation on the axis cylinder after treatment with nitrate of silver. Roudanowsky informs us further that the axis cylinder is knotted, and gives off branches at right angles which anastomose with those ot neighbouring fibres. Fig. 31)1. — Fibrillated structure of the axis cy- linder (after Schultze). a, a strong axis cylinder from the spinal cord of the ox; 6, a nerve fibre from the brain of the electric ray. TISSUES OF THE BODY. 311 §177. We now turn to the cellular elements or the ganglion corpuscles, whose appearance is very characteristic, with the exception of many in the brain and spinal cord, where their boundaries are difficult to define. They may be divided into those withoid processes (fig. 302) and those with processes (fig. 303). To the first-mentioned species the term " apolar" has been applied, and to the latter " unipolar," " bipolar," or " multipolar," according to the number of their ramifications. In every variety of size, from 0*0992 mm. down to 0*0451-0*0226- 0*0018 mm. and even less, we meet with these cellular bodies of spherical, oval, pear-shaped, or renal form. In these are situated spheroidal vesicular nuclei bf 0*0180-0*1090 mm., with a round slightly lustrous nucleolus of 00029-0*0045 mm. Another round point, frequently visible in the interior of the latter—either granular or clear—has been given by Mauihner the name of nucleolulus (fig. 308). Not unfrequently the nucleolus is double, but the nucleus is seldom so. The latter, unlike most nuclear formations, gives Avay comparatively rapidly to the action of concentrated acetic acid. The contents of these cells, probably a species of protoplasm, appears as a tough doughy mass, with numerous minute granules of a protein substance, and in addition to these, fat molecules, soluble in alcohol and Fig. 302.—Ganglion cells from a mammal. A, Cells Fig. 303.—Multipolar ganglion with connective-tissue envelope, from which Re- cells with protoplasm pro- malc's fibres take origin, d, d; a, a non-nucleated cesses, from the grey sub- cell; b, two cells with single nuclei; and c, one stance of the human brain. with two of the latter structures. £, A ganglion cell destitute of envelope. ether, and, not at all unfrequently, particles of yellow, brown (fig. 303), or black pigment (fig. 305, 4). The latter substances offer a most determined resistance to the action of alkalies. All these ganglion cells, the central as well as the peripheral, are destitute of distinct membranes. In the grey matter of the nervous centres they are imbedded in that fibrillated sustentacular substance already mentioned at p. 197. In the peripheral ganglia, on the other hand, of man and the vertebrates, they are usually enclosed in envelopes 21 312 MANUAL OF HISTOLOGY. of a non-fibrillated nucleated tissue (fig. 302, A), from which they may be isolated in the form of membraneless corpuscles (B). According to recent investigations, the internal surface of each of these corpuscles is lined in man and the vertebrate animals with delicate flattened epithelium or endothelium, resembling that of the blood-vessels (Frdntzel, Koelliker, Schwalbe) (1). What is the nature of this enveloping nucleated tissue? Here we meet with a great variety of opinions. It was formerly set down as being in toto a connective-tissue structure, but Beale and Remak ascribe to it a nervous character. Be this as it may, the distinct origin of Remak's fibres from these systems of capsules is very remarkable. Remarks.—1. This was noticed years ago by Robin and R. Wagner in the case of the ganglion cells of the electric ray. Remak too was aware of the presence of this cellular lining. §178. The processes and ramifications of the ganglion cells serve, in the first place, possibly as connections between neighbouring cells (commissural fibres), and, in the next place, they certainly go to form the axis cylinders of different nerve fibres. For the investigation of these very difficult points the hnver orders of vertebrates, and especially fishes, are to be recom- mended, in Avhich the dissection is rendered easy by the small amount of enveloping connective-tissue (1). The following points may be noticed in the nervous knots of the burbot [Gadus lota (2)] (fig. 304). Some of the ganglion cells appear apolar (i, k), no trace even of ruptured processes being discoverable, the appearance of the capsule conveying the impression rather of its being closed. These represent possibly only the earlier stages of development of ramifying cells (Beale). Others, and they are of a smaller kind, are unipolar, giving off at one end a process Avhich assumes, after having run for a certain distance, a darker and more medullated appearance, becpming eventually a narrow nerve fibre (/). On some ganglion cells, though apparently unipolar (e), another ruptured portion of fibre may be recognised on the mutilated envelope. Unipolar cells, continuous through their processes Avith broad nerve tubes, are not met with. Bipolar ganglion cells are of frequent occurrence. The smaller are in communication with narrow, the larger with broad, nerve fibres. The first (d) frequently show us pale fibres of considerable length, which, in the case of the unipolar cell, become transformed into nerve tubes. The latter (a, b, c) present to us the fibre as a dark medullated tube, extending as far as the extremity of the cell (a). Here the medullary matter spreads out in a thin layer, investing the bodv of the latter (3) and may persist in that situation even after the rest of it has escaped from the cut end of the nervous tube (b, c). Such bipolar origins as at h are of rare occurrence, as also the appear- ance of two ganglion cells on one and the same nervous tube as at g Our diagrams show also that the enveloping neurilemma or capsule of the ganglion cell is continuous with the connective-tissue primitive sheath of the nerve tube. In the peripheral ganglia of fishes, multipolar cells do not occur. Even those with three processes, are very rare (Stannius). I he recognition of corresponding structural relations in the human being and among the mammalia is of much greater difficulty, owin" to the larger proportion of interstitial connective-tissue, and mutilated TISSUES OF THE BODY. 313 ganglion cells are also of frequent occurrence here. Xor dare we form conclusions in regard to the mammal body from what is found in the fish. The existence, however, of apolar, unipolar, and bipolar ganglion cells, cannot be denied in this case also after candid consideration, although we are still in the dark as to the relative frequency of the various forms. Multipolar cells must be looked upon as peculiar to many peripheral ganglionic masses, as also to the terminal expansion of the optic nerve in the retina. They Avere discovered by Remak in the sym- pathetic. The same species of, and pos- sibly also exclusively, multipolar ganglion cells, occur likewise in the grey matter of the brain and spinal cord (fig. 305); those apolar specimens Avhich are found here, or such as have only one or two processes, being probably mutilated cells (Wagner, Schroder van der Kolk). These cells, Avhich contain either a pale substance alone (2), or, besides this, brown and black pigmentary particles (4), possess a very variable number of ramifica- tions, ranging from 4 to 20 and upwards (1-4). The latter appear, under high magnifying power, partly as broad or narrow processes of the finely granular cell body (2, c), and partly homogeneous (1, a). Some of these ramifica- tions split up eventually, with repeated subdivision (4), into fibres Df extreme fineness. Others, acting is commissures (2, c; 3, b), are sup- posed to combine the ganglion cells to a physiological unit (4). Finally, axis cylinders are seen arising from them (fig. 305, 1, a, b; 3, c; and 298, g*). It is at present impossible to trace any connection betAveen the variation in the ganglion cells just described, and a difference in function in each or any. Remarks.—1. In older histological Avorks of the year 40, apolar ganglion cells alone were recognised. Purkinje, it is true, had seen the processes of ganglion cells in 1838, but had not recognised their significance. Subsequently to Helmholtz's and Will's discovery ofthe one-sided origin of fibres among the invertebrate animals, Koelliker, was the first to demonstrate its occurrence among the vertebrates. Great progress was next made in this direction in the year 1847, through the discovery, by Wagner and Fig. 304.—Nerve cells from the peripheral ganglia of Gaduslota. a, b, c, Bipolar connected with broad nerve fibres; d, similar cell produced into a narrow fibre; e, another of the same kind, from which a nerve fibre has been torn off; /, an uni- polar cell with narrow tube; g, two bipolar (^-1, g-2) peculiarly united to fine nerve tubes; h, an- other bipolar cell; t, *, two apolar ganglion cells. 314 MANUAL OF HISTOLOGY. Robin, of bipolar cells in the ganglia of fishes. 2. Phil. Trans for the year 1863, vol. cliii. part ii. p. 543. 3. In his excellent treatise (Observationes de retinae structura penitori) M. Schultze divides ganglion cells into four classes, and, as far as our own observation goes, they may be so classed with propriety, though intermediate forms also exist. The four are as follows : (a) those that have neither neurilemma nor medullary sheath, as in the brain, cord, and retina ; (b) such as have neurilemma, but processes (a) becomes the axis cylinder of a nerve fibre (6); 2, a cell (a) connected with another (6) by means of a commissure (c); 3, diagram of three cells (a) con- nected by means of commissures (6), and running into fibres (c); 4, a multipolar cell containing black pigment. no medullary envelope, as in the sympathetic and other peripheral ganglia with multipolar elements ; (c) ganglion cells with medullary envelope, but no neurilemma, of which we see isolated examples in the N. acusticus; and, finally, those which possess both medullary sheath and neurilemma, as in the bipolar cells of spinal gangha. Corresponding to these Ave have four species of nerve fibres, namely, (a) naked axis cylinders ; (b) axis cylinders with neurilemma, but without a medullary sheath, as in the olfactory nerve and Remak's fibres ; (c) axis cylinders Avithout a primitive sheath, but supplied with an envelope of medullary substance, as for instance in the white matter of the nervous centres ; and finally, (d) axis cylinders surrounded by both medulla and primitive sheath, the usual form. 4. Strange to say, the existence of commissural fibres between the central ganglion cells is stoutly denied by Dexters. I myself have seen them most certainly many years ago, and believe in them still. §179. Here also, as in the consideration of the nerve tubes, the question arises, Does the description of the ganglion cell just terminated give us its complete structure, or does it possess a finer texture1? At present the extremely various views on the subject supply us with but very inadequate materials for replying to this query conclusively. Thus the nerve fibre, i.e., the axis cylinder, has been stated to spring from tho nucleus or nucleolus. Among the various observations made on this TISSUES OF THE BODY. 315 point there are doubtless some feAV which are correct (always excluding those based on optical illusions), but they are probably the exception (IV One discoA-ery made by Beale some years ago, on the other hand, we do look upon as correct, having satisfied ourselves further by personal observa- tion. It applies to the ganglion cell of the tree frog (fig. 306). Here may be seen, namely, making its exit from the interior of the pear-shaped or round structure, at its pointed end, a straight fibre, in which a nucleus (c, e) is not un- frequently visible. This is surrounded by the coils of one or more spiral fibres, which also contain nuclei. These spring from the surface of the cell-body in close spiral turns (d, d), which increase in girth as they proceed on their way round the straight fibre, until they eventually attain a straight course them- selves, and pass on as spinal fibres with their own special sheath (/). The first mentioned fibre, which, as has been already mentioned, springs from the in- terior of the cell-body (whether from the nucleus or no we are unable to say Avith certainty), is of nervous structure. Beale maintains also that the spiral have the same character, though they appear to us to be, as a rule, of elastic nature. But we are far from denying the pos- sibility that, when two fibres spring from the one pole of a ganglion cell, one of them may encircle the other spirally. J. Arnold maintains that these cells possess a much more highly complicated structure. Deiters mentions having found a double mode of arrangement in the ramifications of the cells of the nervous centres (fig. 307). The greater number of the processes is formed, namely, by prolongations in various directions of the protoplasm composing the body of the cell. These "protoplasm processes" then undergo repeated subdivision, giving off branches in all directions, until they finally dip into the sustentacular matter in the form of the most extremely delicate fibrillae. From these protoplasm ramifications Ave can distinguish at a glance one peculiarly long process (a), Avhich springs either from the cell itself or from one of the first and broadest prolongations of its body. This pro- cess never gives off branches, and becomes clothed later on wdth a medullary sheath ; it is known as the " axis cylinder process." Of the correctness of this avo may easily convince ourselves. Beside these just mentioned, other very fine fibres may be recognised (b, b), leaving the protoplasm ramifications at right angles. In these Deiters supposes (without, however, giving any reason for his opinion), that we have before us a second system of extremely fine axis cylinders. Fig. 306.—Ganglion cells from the sympa- thetic of the tree frog (from Beale). a, cell-body; b, envelope; c, straight nervous fibre; d, spiral fibres; e, continuation of the former; and /, of the latter. 316 MANUAL OF HISTOLOGY. According to Schultze's recent investigations, both forms of processes of these central ganglion cells (fig. 30*8) possess a fibrillated texture, more apparent in the axis cylinder processes (a) than in the protoplasm ramifi- cations (b), in which latter a granular interstitial substance is present in considerable quantity. All these primitive fibrillae may be followed up Fig. 307.—'Multipolar ganglion cell from the anterior cornu of the spinal cord of the ox, with an axis cylinder process (a), and other protoplasm processsa with their ramifications, from which the finest fibres take origin (after Deiters). into the body of the ganglion cell, and may be easily recognised there, especially in the external portions, imbedded in a finely molecular mass. Their course is a complicated one, sometimes diverging on entry, and sometimes giving rise to an interlacement of crossing and re-crossing fibrillae. Connection with the nucleus or nucleolus does not take place. Whether we have here the true origin of the primi- tive fibrillae, or whether the latter merely undergo a re-arrangement here,—that is, that, arriving from remote localities through the various TISSUES OF THE BODY. 31' protoplasm processes and penetrating the body of a cell, they are collected together in the latter, and pass out as an axis cylinder,—are questions still undecided. Fig. 308.—Ganglion cell from the anterior cornu of the spinal cord of the ox (after Schultze). a, axis cylinder; b, processes sent off by the cell. Remarks.—See Beale's treatise in the Phil. Trans, for the year 1863, part ii. p. 543. Many other German observers agree with us in our view of the probably elastic nature of the spiral fibres. §180. Having become acquainted Avith the tAvo kinds of form-elements of the nervous system, let us noAv turn to the consideration of their general arrangement in the peripheral nervous apparatus. The nerves of the brain and spinal cord, differing in their white colour from those of the sympathetic system, Avhich are usually grey or greyish red, become clothed Avith a delicate envelope at their exit from the nervous centres. This covering receives another addition from the dura mater of connective-tissue bundles in its passage through the latter, and, thus strengthened, constitutes what was formerly known as "neurilemma," but which we will designate from henceforth "perineurium" (1). 318 MANUAL OF HISTOLOGY. Internally this perineurium extends between the bundles of nerve-fibres, Avhich, as in muscle, may be divided into primary and secondary, and in Avhich the tubes are already arranged in the series in which they even- tually leave the trunk. In some cases the connective-tissue preserves its fibrous character, especially when it binds together larger collections of nervous tubes than usual, whde around the primary fasciculi it appears rather as a homogeneous nucleated substance. Again, having become modified to a homogeneous material, it enters into the formation of the primitive sheaths around the medullary portion of the nerve-tubes con- tained in the trunk. Finally, the latter is traversed by a scanty network of capdlaries, consisting of fine tubes measuring about 00056 mm. From the fact that the primitive fibres run along side by side unchanged in the nerve, without giving any indications as to their functions by their appearance, all branchings, anastomoses, and formations of plexuses, may be regarded by the physiologist Avith tolerable indifference. As is Avell known, there occurs a progressive splitting up of the nervous trunks at very acute angles in their course towards the periphery. Thus, the primitive tubes leave the stem or common path in bundles, and, bend- ing off sideways, pursue their way separately towards the organs they supply. The actions of the \*arious nerves is, however, by no means determined by this arrangement; but in one made up of sensitive and motor fibres, this formation of branches may bring about a separation of the latter. Anastomoses, for the interchange of different kinds of fibres for anato- mical ends, are connections between neighbouring nerves or branches of the latter. We may distinguish betAveen simple and double anastomoses also. In the first, a number of nerve-tubes pass through a connecting branch into another trunk, pursuing in this their further course; in the second, both nerves exchange fibres with one another. This interchange of fibres between adjacent nerves, Avhen it takes place to any great extent, gives rise to the so-called plexus. These branchings, anastomoses, and formations of plexuses, are con- tinued down to nerves of microscopic minuteness, and even in the organs within Avhich the latter are to terminate. In them especially the formation of plexuses is a very general occurrence just before the final radiation of the fibrillae, and has been alike described in earlier and more recent times. In the larger and more massive plexuses an interchange of single primitive fibres alone is to be observed ; while in the finer, or, as they have been called, the terminal plexuses, repeated divisions of the nervous tubes and retiform intercommunications betAveen their branches have been met with. In its Avhole course, from its central origin until towards its peripheral distribution, the nerve fibre does not change its character in the least, and its diameter but to a slight degree. With the progressive division of the nervous trunk, however, certain modifications of the connective-tissue sheathing make their appearance. This latter, namely, decreases in amount from the stem toAvards the branches, and appears no longer fibrillated on the finer twigs, but only streaky, until, finally, in the terminal filaments, Ave find nothing but a homogeneous nucleated mass. This simplest form of perineurium may be seen on little twigs Avhich only contain a few primitive fibres. Even single nervous tubes may course through a tissue for a considerable dis- tance in a clothing of this kind, until they terminate finally with loss of TISSUES OF THE BODY. 319 the latter. In such cases the connective-tissue envelope is perineurium and neurilemma at the same time. These facts, however, are variously viewed, some regarding this simplified perineurium as a thick primitive sheath. The trunks and branches of the sympathetic system are essentially the same in structure as those just described, except that in them Remak's fibres (already mentioned at § 176) make their appearance in great numbers. Remarks.—This name was first applied by Robin to the envelopes composed of simple connective-tissue of the finest twigs. §181. From time immemorial anatomists and physiologists have been occu- pied with the question, how the nervous fibres terminate peripherally. In older times, of course, before the introduction of microscopic analysis, conjecture alone could be formed on this point. It was supposed that the nervous tAvigs broke up into finer and finer fibrils, Avhich became fused finally with the tissue of the organ they supplied. With the aid of the microscope, about the thirtieth year of this century, it Avas already a matter of no difficulty to follow the progressive sub-division of the smaller branches down to their finest tAvigs, and to recognise here and there the course of the latter through the tissue, as well as the formation of the plexuses and minutest anastomoses already mentioned (§ 180). At that time many observers maintained that they had found a looped termination, and, moreover, in the most different organs. • They supposed that two neighbouring fibres Avere always united at the peri- phery in the form of a Avider or narrower loop, or, what is but another mode of expressing the same thing, that each nerve tube, on arriving at the periphery, became doubled on itself, and took its course back again to the nervous centre, from Avhence it came. This theory of terminal loops, which held good for motor and sensitive fibres alike, led hoAvever to great physiological difficulties. We now know, from a series of newer and more accurate investigations, that these loops are of frequent occurrence among the peripheral ramifica- tions of nerves, but that they possess no terminal significance, since the nerve fibre in this curved course has not yet arrived at its final destina- tion. This theory of the looped termination of nerves has, therefore, disappeared from histology. As far as Ave knoAV at present (though our knowledge on the subject is still in a most unsatisfactory condition), nervous fibres terminate Without any medullary substance—first of all in the form of simple or ramifying axis cylinders, and, in the next place, in the form of primitive fibrillce. The final disappearance of the fibre, moreover, is frequently seen to take place in special "terminal structures" or "end corpuscles." These are either complex or single-celled. §182. It was for some time supposed that an insight of the mode of termina- tion of the motor nerves in striped muscle (fig. 309) had been gained Avith tolerable correctness through the labours of R. Wagner and Reiehert (1). It Avas believed that the motor nerve tube ceased on the striped fibre after repeated sub-division in the form of pale terminal filaments. On account 320 MANUAL OF HISTOLOGY. of this repeated splitting-up of the primitive fibres further, a considerable number of terminal filaments could be formed from a feAV of the latter (2). So far the difficulty of folloAving up the nerves is but small, if A\-e take, for instance, the platysma of the frog. But experience teaches that this repeated division of motor nerve fibres is peculiar to the lower orders of vertebrate animals. In fishes also it may give rise to the formation of more than one hundred terminal filaments from one such ; and primitive fibres are by no means rare, which supply upAvards of fifty muscular fibres. Among the higher orders of vertebrata, on the contrary, this splitting up becomes less and less frequent, so that its occurrence is only excep- tional among the mammalia. The number of muscle and nerve fibres becomes almost the same,—a fact of great physiological importance. If we examine one of the thin transparent muscles of a frog, we find without any difficulty the small trunks of the nerves, Avhich have entered the substance of the latter, lying sometimes obliquely, sometimes parallel to its fibres, and giving off numerous branches and anastomotic twigs. In human and mammalian muscle likewise a plexiform interchange of fibres between adjacent twigs may be observed. At the points of division of the latter, and especially when they have attained a considerable degree of fineness, and contain but feAV primitive fibres, Ave not unfrequently perceive the manner in which a nerve-fibre suddenly breaks up into two or more branches, with a contraction generally at the point Avhere the latter part from one another. These branches possess the same medullated appearance as the parent stem, and pass onwards, according to the character of the Avhole nerve, more or less divergent. Deceptive appearances, hoAvever, are matters of possibility here. At those points, hoAvever, Avhere, in the further course of their ramifica- tions, the nerve fibres come to lie either singly or in extremely small number together, traversing thus the muscle in a usually oblique direction (309, a), their further subdivision may be most distinctly observed. This most frequently occurs by division into two threads, more rarely into three or four. The latter may either correspond to one another in breadth, or are unlike in that respect (a beloAv and in the centre). Con- tractions at the points of division may not be present, or if so, only slightly marked; or again, they may be very strongly pronounced. But complete solution of continuity, to such an extent that the empty primitive sheath alone remains, is always an artificial production. The axis cylinder, on the other hand, divested entirely of medullary sheath, appears frequently as a natural formation. The division of this axis cylinder is for the rest hardly anything more than the separation of the original primitive fibrillae" into two neAv fasciculi of smaller diameter. In consequence of this repeated division, the nerve fibres (which possessed at the outset a medium diameter of 0*0142-0*0113 mm. and a double contour) become gradually reduced in calibre down to 0*0056 mm., and lose their double outline (b). Finally, however, Ave observe the terminal twigs of 0*0045-0*0038 mm. in breadth approaching the single muscle fibres in the form of free axis cylinders having lost their dark medullated appearance, and apparently ending here in tAvo short branches. It was formerly believed that we had here in these pale fibres the truo termination of the nerves, while it still remained a matter of uncertainty, TISSUES OF THE BODY. 321 owing to the difficulty of investigation, whether this took place externady on the sarkolemma, or after perforating the latter in the interior of the fleshy substance. Fig. 309.—Distribution of nerves in a voluntary muscle from the frog. a. a nei ve fibre destitute of neurilemma, showing repeated subdivision down to apparently terminal filaments b, b; c, an undivided nerve fibre with a thick envelope. From a whole series of recent investigations, among which those alone of Beale, Kiihne, Margo, Koelliker, Krause, Rouget, Engelmann (3p need here be mentioned, the conclusion has been arrived at that this early view is likeAvise untenable, and that the true ending of the fibres takes place far beyond these apparently terminal tAvigs. But in Avhat form and where this final cessation of the fibre is situated, Avhether within or external to the sarkolemma, is a point about which considerable difference of opinion still prevails. Beale, Krause, and Koelliker believe the fibre to terminate externally, Avhile the other observers are of the opinion that it perforates the sarko- lemma ; and Ave believe rightly. In fact, we may see, on examination of the muscular fibres of verte- 322 MANUAL OF HISTOLOGY. brates (fig. 310), that the dark-edged primitive fibre (a, b) approaches the muscle fibre (g, left), enclosed within a loose nucleated sheath (c, d), and pierces the sarkolemma, Avhile the neurilemma becomes continuous with the latter (c, left). Beneath the sheath of the muscle the terminal filament swells up into a finely granular mass of a flattened form containing nuclei (/, left). This merges at its edges (e, e), and concave under surface, into the fleshy substance of the fibre (4). To this structure in which the fibre ends, and Avhich occurs only singly in mammalian muscle fibres, has been given the very appropriate name of " terminal plate " by Krause, Rouget, Engelmann, and others; while Kiihne calls it the " neural emin- ence " (Nervenhiigel). In the mammalian body, in which these terminal plates are Avell developed, and occupy a not incon- siderable portion of the sur- face of the muscle fibre, their diameter ranges from 0*0399 to 0*0602 mm., while in thickness they vary. Their nuclei are smooth, clear, oval, and contain one or two nucleoli, thereby dif- fering from the more opaque formations of the neuri- lemma, and likewise from those of the muscular fibres. In diameter they range from 0*0049 to 0*0099 mm. Their number is liable to variation • from four to twenty being found in one plate. Terminal plates of the same kind are to be met with in birds and reptiles. But a number of questions relative to the nature of these neural eminences must for the present be left unansAvered, and perhaps for a long time still; for instance : Do we see in them the Avhole of the ultimate distribution of the fibre ? Does the finely granular substance of which they are composed take its origin from a transformation of the axis cylinder, or does the latter end within them, and, if so, in Avhat form? On these points there is no lack of variety of opinion. According to Krause, we may recognise a pale, single, double, or triple fibre (axis cylinder) within the terminal plate, ending with a swelling or knob upon it. A very fine and somewhat tortuous fibre was also remarked in the same situation by Schbnn. But from Kiihne's researches which from our own observations we are inclined to regard as correct we learn that the structure is far more complicated. On its entrance 'into the terminal apparatus (fig. 311), the axis cylinder of the nerve fibre divides, and spreads out with further ramification into a peculiar palp Fig. 310.—Two muscular fibres from the psoas of the Guinea pig, showing terminations of n«rves. a, b, the primitive fibres with their transition into the terminal plates e,f; c, neurilemma with nuclei a\ d, continuous with the sarko- lemma g, g; h, muscle nuclei. TISSUES OF THE BODY. 323 Fig. 311. — A muscle fibre from the lizard, a; b, nerve fibre; c, dichoto- mous division in the terminal plate, with transition into the true terminal structure of Kiihne. formation, bounded by undulating lines and truncated processes. This is the " true terminal plate." The nuclei and finely granular substance of the "neural eminence " are situated beneath this struc- ture, adjacent to the fleshy mass of the fibre (5). Engelmann also speaks of an ar- borescent arrangement of branches of the axis cylinder lying in the granular sub- stance of the neural eminence. Now if, as Avould appear to be the case, the distribution of the nerve fibre be confined to the immediate mass of the terminal plate, the extremities of the muscle fibre must remain without nervous supply, in that the former is set into the latter at about its middle. But the fleshy matter manifests contractility at the ex- tremities also ! The bearing of the terminal portions of the nerves supplying the muscles of the lower orders of vertebrates, of naked amphibia and fishes, present new difficulties in this so uncertain, but phy- siologically so important subject. Here we find that those complex mul- tinuclear terminal plates are no longer present. In the frog, the nerve tube, on arriving at the fibre, not unfrequently breaks up into a multitude of dark-edged fibrils, forming thus the " terminal tuft" of Kiihne. These having pierced the sarkolemma, course along within the muscle fibre as intramuscular axis cylinders Avith isolated nuclei, and eventually become merged, to all appearance, in the fleshy mass. Whether Ave have to deal here with simple uninuclear terminal plates (Krause, Waldeyer) (of which, in that case, several Avould seem to be present in one muscle fibre), or whether this system of intramuscular axis cylinders may not represent in the frog the true terminal plate of Krause, mentioned above, are questions Avhich must be determined by future research. According to Krause, these terminal plates are to be found also in the heart of the rabbit. Taken from other sources, the results which have been obtained on inquiry into the nature of the final terminations of nerve fibres are essentially different. Remarks.—1. /. Miiller and Briicke appear to have been the first who observed division in the nerve fibres supplying muscle, in the year 1844. 2. Thus Reiehert counted 7-10 afferent nervous fibres in the thin platysma of the frog, containing about 160-180 muscular fibres. These split up, eventually, with progressive rami- fication, into 290-340 terminal filaments. 3. With regard to the final distribution of nerves, modern literature is very rich. Compare, besides the works of Continental investigators—of Kiihne, Rouget, Koelliker, Engelmann, and others—Beale (Proceed- ings ofthe Royal Soc, vol x. p. 519 ; Phil. Transact, for the year 1861, p. 611 ; and 1862, Pt. 2, p. 889 ; also his Archives of Med., No. 11, p. 257 ; and in the Quart. Journ. of Micros. Science, 1863, p. 97; Proceedings, p. 302; and lastly (1864), Transact, p. 94. 4. This is most beautifully seen in the group of small spider-like animals, the tardigrades. Here, where many years ago the terminations of the nerves, i.e., the neural eminence or terminal plate, had been recognised by Doyere, the naked nerve fibre applies itself to the likewise membraneless muscle fibre, and both masses become fused one into the other at the point of contact. If we now suppose both nerve and muscle fibre enclosed in their sheaths, we obtain the same relation of parts as in the mammal body. 5. According to Rouget, the neural 324 MANUAL OF HISTOLOGY. eminence is not the true terminal structure. The nerve fibre, he says, becomes forked (among the arthropods) at the summit of the eminence, giving off two fibrils. These latter then travel the substance of the terminal plate, and breaking up into numerous filaments, end in the fleshy mass of the muscular element. 6. According to Beale, there is situated on the exterior of the sarkolemma a very fine nucleated network of nervous elements, to which formation this English investigator ascribes just as little terminal significance as elsewhere in the body, in that the nerves are only spread out peripherally in loops. A similar view of the subject had been pre- viously taken by Schafhausen. The statements of such a man as Beale, however, and the peculiar methods of investigation made use of by him, deserve more con- sideration than has as yet been given them. Koelliker's views, as regards the termina- tion externally upon the sarkolemma, correspond with those of Beale. On the other hand, he only recognises pale terminal fibres in the frog, which he regards as con- tinuations of the axis cylinder and primitive sheath, and which probably end, as a rule, naked. He encountered, however, some isolated cases, which seemed to indicate a termination in a very fine dense network. Margo's views, on the other hand, are completely different. According to him, the nerve pierces the sarkolemma, sinks into the fleshy matter, and is in communication here with a peculiar terminal apparatus. The latter he looks upon as formed of the greater part of the muscle nuclei and the network of the so-called interstitial granular threads (§ 166). §183. Turning now to unstriped muscular tissue, we find it far more difficult to recognise in it the final distribution of the nerve fibres than in the tissue Ave have just been considering. Division occurs here also, as has been seen, for instance, in the stomach of the frog and rabbit by Ecker; in the heart of amphibia and nerves supplying the uterus of rodentia by Kilian. In the mesentery of the frog (fig. 312), moderately treated Avith acetic acid, we may observe in the narrow medullated nerve fibres enclosed in a thickened envelope several repeated dichotomous divisions, until at last the branches penetrate the walls of the part and are removed from further observation. These fibres are enclosed, as Avas before indicated, in a thick nucleated envelope. But what becomes of these nervous elements on arrival in the unstriped muscular tissue 1 This is a question which for a long time remained Avithout any satis- factory answer. It is true that years ago plexuses or netAvorks of pale delicate filaments had been met with, with nuclear structures at the expanded nodal points, and that this netAvork was held by many to be a terminal structure, which view seemed strengthened by the fact of the occurrence of a similar nervous end-formation in the electric organs of the ray. But not long ago an important discovery apparently was made by Frankenhduser, subsequently confirmed by Lindgren, and more recently still through the most comprehensive researches by Arnold. This Avas that the nerve fibres of smooth muscle penetrate to the nucleus of the contractile cell in the form of a fine terminal filament, the primitive fibrida, and end probably in the nucleolus. From Arnold's experiences it would appear that the nervous twigs sup- plying unstriped muscle consist partly of medullated and partly of non- medullated fibres, in varying proportion. We encounter the latter as fine or broad threads, measuring in diameter 0*0018-0 002 mm , and showing at intervals small nuclei. Externally, in the connective-tissue covering the muscle, these nerves are arranged in the form of a wide- meshed network, in which, as Beale has pointed out, ganglion cells are to be found at certain points in the muscles of the vascular system To this the name "ground plexus" has been given (1). TISSUES OF THE BODY. 325 From this plexus are given off, in the first place, medullated nervous. fibres, which assume, after a longer or shorter course, the form of pale longitudinally striated bands of 0*0041- 0 0050 mm. in diameter, con- taining at intervals nuclei of the same dimensions. These bands become gradually nar- rowed down until we meet them as the nucleated fibres, 0*0018-0*0023 mm. in dia- meter, Avhich have been already mentioned. From these, again, is formed a second network Avith toler- ably broad rhomboidal or elongated meshes, Avhose no- dal points show nuclei Avith distinct nucleoli. Pale fibres, however, are also given off directly from the "ground- plexus " to the muscle cells. This the "intermediate net- work" (fig. 313) lies imme- diately upon the layers of mus- cular tissue, or between the latter penetrate between the muscle fibres at the commencement, and become rapidly smaller, so that after repeated subdivision they are reduced to threads of 0*0005-0*0003 mm. in thickness. On the latter, as Avell at their point of division as elsewhere, there occur elliptical, round, or other- Avise shaped swellings or granules. The last-mentioned fine fibres unite once again to form a new, but this time very close-meshed netAvork, the "intramuscular," Avhose varicose fib- rillae occupy the narrow passages be- tween the contractile cells. Finally, leaving this intramus- cular interlacement, dark straight fibres of extreme fineness pass off, which are at the very most 0 0002 mm. in thickness. These penetrate into the contractile cells, and ad- vancing to the nucleus, terminate, according to Frankenhauser, in the nucleolus. The number of terminal filaments Avhich enter any one muscle cell corresponds with the number of granules occurring in the nucleus (§ 163). Fig. 312.—Two narrow branching nerve fibres (a, b) from the mesentery of the frog, surrounded with a thick nucleated envelope. At 1, the trunks; at 2 and 3, the branches. From it there pass off small fibres which These are only supplied with nuclei Fig. 313.—Ramification of nerves and termina- tion in the muscular tunic of a small artery of a frog; from Arnold. 326 MANUAL OF HISTOLOGY. Arnold believes, however, that in very many cases these fibrillar leave the nucleoli again in an opposite direction, and after having traversed the nucleus and body of the cell, unite once more Avith the intramuscular network. According to this, the nucleolus Avould appear to be not the terminal point, but only a knot on the ultimate filament. Later on we shall have to discuss the reticulum of the corneal nerves. We must now turn to the consideration of the nerves supplying glands, which were discovered by Krause. Here, besides dark-edged fibres which occur in the salivary and lachrymal glands of mammals, and come to an end in peculiar terminal structures, to be referred to again ; besides these, pale nucleated nerve fibres, only about 0*0020 mm. in diameter, may be remarked between the glandular follicles, and applied, with dual division, to the so-called membrana propria of the gland element. These fibres just described take their origin from dense netAvorks of medullated tubes situated around the excretory ducts of the lobules. Finally, it is stated by Pfiiiger that in the salivary glands the delicate end filaments of the nerve fibres terminate in the gland-cells after piercing the membrana propria. He has also seen the processes of multipolar structures, lying external to the follicles, coming to an end in the same. These he supposes to be ganglion cells. The same observer states that a similar arrangement of parts is to be seen in the pancreas. In the liver also he has found a connection between the nerve fibres and gland cells. Between the cells likewise of the lacrymal gland, a radiation of fine terminal fibres has been described by Boll. We regret being obliged to express our incredulity as regards the correctness of all these statements; in our opinion, the termination of the nerve filaments in glands is still unknown. Remarks.—Philos. Trans, for the year 1863, part ii. p. 562. §184. The final destination of the sensory nerve fibre, to Avhich we now turn, is found to be in the first place a special terminal structure—the extremely abstruse and much-disputed question of their bearing in most of the organs of special sense Ave leave out of the question—in the next place, it seems probable that the fibre may end with free ramifica- tions. The best known anatomical recipients of the sensitive nerves are—(1) the Pacinian bodies; (2) the tactile corpuscles of Wagner and Meissner; and (3) the terminal bulbs of Krause. The first of these, the oldest discovery, present the greatest complexity of structure; the last or neAvest, the least. The terminal bulbs of Krause (fig. 314) are found in the human being on the sensitive nerves of the mucous membrane and in the skin. They are met Avith again in the conjunctiva bulbi, in the mucous membrane at the base of the tongue, in the fusiform and circumvallate papilla? of the latter, and in the soft palate, glans penis and clitoris. In the mam- malian body they are also Avidely distributed. They have been also met with in the external skin, as, for instance, in that of the mouse, and they occur on the volar aspect of the Guinea-pig's toes. Their nature, moreover, is the same in the mammalia as in our own frame. The form of these structures in the mammal is egg-shaped (1, a), 0*0751-0*1409 mm. in length, and (2 a) about one-fourth as broad.' In man and the monkey they are more rounded, their diameter beincr from TISSUES OF THE BODY. 327 > \2 0*0322 to 0*0751 mm. Some isolated bulbs may attain, hoAvever, much greater dimensions, and twisted or indented forms are also met with. The terminal bulb of Krause consists of a transparent nucleated envelopo, containing a soft, homogeneous, slightly lustrous substance. The nerves connected with it (c) undergo subdivision into branches more or less frequently repeated (1*, 2). Thus from one primitive fibre from 6 to 10 terminal corpuscles may be supplied. On entering the latter, the pri- mitive fibres of medium size until there (about 0*0046-0*0075 mm.) become imme- ately still finer, constituting then the pale, non-medullated end filament or axis cylin- der (1 b). The latter is 0*0039-0*0029 mm. in thickness, passes through the axis of the structure, and ends towards its upper pole Avith a slight button-like swelling about 0*0046 mm. across. The terminal bulbs of the human con- junctiva (2) frequently present sinuosities and tAvists on the primitive tube as it is about to enter or has already entered the former. These may be present to such an extent as to form a regular convolution, especially in the interior of the corpuscle. Within the latter itself, or before its en- trance, a splitting of the nerve tube may take place; beside which many varieties are to be seen as regards its bearing. The number of these formations also seems to vary considerably. In 1 Q'" of the conjunctiva of the calf Krause noticed 13 terminal bulbs. Structures allied to the latter Avere also met with by Krause in the glans clitoridis, and in smaller number in the penis. These " genital nerve-corpuscles" lie in the tissue of the mucosa at the bases of the papillse of the mucous membrane. In size and form they vary, some of them attaining a diameter 0*1439, or even 0*2001 mm. As a characteristic of these genital nerve-corpuscles, constrictions may be mentioned which occur in varying number on the surface, and com- municate to the Avhole a mulberry-like appearance. They appear to be the recipients of sexual sensation, for which reason Finger proposes giving them the name of "sensual corpuscles" (Wollustkdrperchen). The same observer has described another kind of structure similar to the end-bulbs, as present in the racemose glands of mammalia. These, the " end capsules of the gland nerves," have a somewhat elliptical form, and consist of a number of concentrically laminated membranes, from four to eight of Avhich may be observed in each, and which are studded with numerous nuclei. In the interior is to be seen the minute cylin- drical end-bulb, Avhich is not unfrequently of sigmoid figure, and whose axis is occupied by an almost immeasurably fine lustrous terminal fir re. The latter springs from a dark-edged nerve tube. 22 Fig. 314.—Terminal bulb. 1. From the conjunctiva of a calf. 2. From that of a human being, a. Bulb; c, nerve fibre ending in (1) an axis cylinder (6). 328 MANUAL OF HISTOLOGY. §185. Another modification, to a certain extent, of these end bulbs of Krause is presented to us in the tactile or touch coipuscles of the skin (fig. 315). The nervous network supplying the latter give off primitive fibres towards the bases of the so-called tactile papillae (p. 234), Avhich pass Fig. 315.—Vertical section of three groups of tactile papillae of the human index finger, occupied partly by vascular loops, and partly by tactile corpuscles. forward either isolated or lying together in small fasciculi of microscopic fineness. Here division of the nervous tubes, at acute angles, occurs with great frequency. These touch-corpuscles may be found on the volar aspect of the fingers and toes, and on the palm of the hand and sole of the foot. Their number is greatest on the aspect of flexion of the last joints of the fingers, and decreases then from the second to the first. In the palm of the hand they are still fewer in number. Thus in the □'" to 400 papillse, 108 tactile corpuscles were found by Meissner on the last joint of the finger, whde in the second joint the latter only amounted to 40, on the first to 15, and in the palm of the hand to 8. Their amount is also most con- siderable on the last joint of the toes. Here, however, the proportion, as compared to the hand, is very small. On the back of the hand, the dorsum of the foot, and volar surface of the forearm, we may also en- counter a few of these tactile corpuscles. Krause has found them, besides, in the conjunctiva. Finally, they are to be met with in the nipple and skin of the lips, though in but moderate number. In the latter regions intermediate forms betAveen them and the terminal bulbs have been described. Among the mammals they have only been recog- nised in the ape, in the palm of the hand, sole of the foot, and skin of the lips (Meissner, Krause). Size and form are liable to considerable variation. In the vola manus they measure upwards of 0*1115 mm. with a breadth of 0*0451-0*0563 mm. Smaller specimens may only reach 0*0451-0*0377 mm. Those of greater dimensions are usually oval; those of smaller, mostly of rounder figure. These structures are situated in the axis and apex of the tactile papillae, but excentrically in those which are in any degree complex. Only the latter are exceptionally supplied also with vascular loops (fig. 315 ; in the middle a double papilla). Otherwise those which contain tactile cor- puscles are non-vascular. The touch corpuscle consists of a capsule formed of a homogeneous substance enclosing a finely granular soft matter best seen in transverse section. In the capsule, further Ave may remark numerous elongated bodies arranged transversely or obliquely. We shall refer to these again pre- TISSUES OF THE BODY. 329 Fig. 316—Two human tactile papillae from the volar surface of the index finger. In the interior we have the tactile corpuscles, into whose tissue the nervous fibres may be seen entering. sently. They communicate to the whole structure a characteristic trans- versely striated appearance. The nerve fibres (fig. 316) pass out towards these bodies either singly, or, as is more frequently the case, double: at times, also, they are trebled or quadrupled. They are enveloped in simple neu- rilemma (fig. 316), which is con- tinuous with the capsule. They are dark-edged, 0*0045 mm. and less in breadth, and enter the base of the touch-corpuscle, or at times also its side. The mode in Avhich they end, however, is difficult to determine. At times a peculiar twining of the nerve tubes around the tactile cor- puscle may be remarked, or they may be seen to run for a greater or less distance straight along the latter. They all finally pass into the interior of the corpuscle, however, but in what manner they end there is still unascertained. In all probability they spread out in the form of pale non-medullated fibres or axis cylinders, like those of the terminal bulb. That the transversely arranged nuclear bodies, already mentioned, are con- nected with the termination of the fibrillae appears extremely improbable. §186. We turn now, in conclusion, to the Pacinian bodies, which may be likened to a terminal bulb enveloped in numerous concentric capsules of connective-tissue. As they come under our notice they are elliptical structures, sometimes more elongated than at others, and measuring from 1 to 2 mm. in length. To the unaided eye they appear translucent, and marked towards the axis Avith a streak. In man they occur regularly on the nerves supplying the palm of the hand and sole of the foot, but Avith especial frequency on those passing to the tops of the fingers and toes. Their total number, in these parts taken together, has been estimated at from 600 to 1400. According to Rauber, they are met with also, but with less frequency and constancy, at many other points in the body : thus on the dorsum of the foot and back of the hand, beneath the skin of the arm, forearm, and neck; on the intercostal nerves, and all the articular nerves of the extre- mities. They are likeAvise to be found on many nerves supplying bone, and in the interior of the muscles of the hand and foot; further, in the nerves of the parts of generation, and finally on the plexuses of the sym- pathetic system, round about the abdominal aorta. Again, they are encountered among the mammalia; especially on the sole of the foot, and with exquisite distinctness, and in greater or less number, in the mesentery of the cat. Pacinian bodies are also found in birds as well as in mammals, although modified to a certain extent. The lamina? of the capsules are looked upon as formed of connective- tissue, consisting of an either homogeneous or somewhat fibrillated 330 MANUAL OF HISTOLOGY. ground substance, in Avhich elongated nuclei or cells are imbedded On the internal surface of these membranes a mosaic marking, like epithelium, has been recently remarked by Hoyer after treatment with nitrate of silver. These systems of capsules, fur- ther, are traversed by a scanty vascular netAvork. The individual laminae of Avhich they are composed folloAv the contour of the whole corpuscle, and are not so thick outAvardly as within, where they appear more condensed, and where they sur- round in shorter curves the canal or in- ternal bulb occupying the axis. The latter consists of a soft nucleated connec- tive substance. The internal bulb (c) is rounded off at its termination. Its Avails, like those of the capsules, are continued at the oppo- site extremity into a stalk (a), by which the Pacinian body is attached like a berry to the nerve. This style consists of ordinary longitu- dinally marked connective-tissue, and is formed by the perineurium of the afferent nervous fibre. The diameter of the latter is 00142- 0*0113 mm. and less. It presents the usual medullated appearance, and so reaches the corpuscle, at Avhose inferior pole it makes its entry into the central canal, occupying the axis of the latter. On entering the central passage the fibre loses its dark border, as is the case in the ter- minal bulb of Krause; it then becomes considerably diminished in size, and comes to an end as a pale terminal filament or axis cylinder of dis- tinctly fibrillated constitution. The latter traverses thus the whole internal bulb, and ends at the roof of the latter (c, above) with a slight button-like SAvelling. Division of the nerve fibre before its entry may occur; and not unfre- quently do we see, too, the pale terminal fibre splitting into two or three branches, divisions in Avhich the axial canal may also participate. Very rarely two nerve fibres are seen to enter the same corpuscle, and terminate singly or doubly in a single internal bulb (Koel- liker). Fig. 317.—Pacinian bodies from the mesen- tery of a cat. a, a nerve with its peri- neurium forming the stalk; 6, the system of capsules; c, axial canal or internal bulb, within whicli the nerve tube ends forked. Many other variations besides those mentioned here must be passed over. That these Pacinian bodies are connected with the sensory-nervous apparatus can hardly be a matter of earnest doubt any longer, since the discoveries of Wagner, Meissner, and Krause. Remarks.—These Avondrous structures were known even long ago, but they received but little attention. The old German anatomist Vatcr observed, more than a century ago, that the nerves of the skin of the palm of the hand and sole of the foot were studded not unfrequently with small oval swellings, to which he gave the name of papillce nervce. Later on, in the year '30, after having been completely forgotten for some time, they were again discovered by Padni of Pistoja, and noticed also at the same time in France. They Avere, however, specially brought into notice through a monograph by Henle and Koelliker, which appeared in the year 1844. TISSUES OF THE BODY. 331 These two observers gave the coipuscles the name of Pacinian bodies, Avithout any idea of their previous discovery by Vatcr. This name has been retained by some, while by others the structures are designated as Vater-Pacinian corpuscles. §187. Having finished the consideration of these terminal bodies, let us noAv turn to the question as to how the remaining wholly sensible nerves end, one of the most obscure subjects in minute nervous anatomy, and one about which much uncertainty still prevails. It is quite obvious that centripetal nerves must occur in voluntary muscle as recipients of muscular sensation. Our acquaintance, however, with them, is still very slight. With a view to throAving some light on this point, the platysma of the frog was subjected by Koelliker to minute investigation, being peculiarly well suited for this purpose. Here there is to be seen—possibly springing from the division of a single broad nerve tube—a slight nervous ramifica- tion, confining itself almost entirely to the anterior surface of the muscle. The narrow nervous twigs of the same are, at their commencement, still dark-edged, but become paler as the branching progresses, and are seen later on as fibrils clothed with a loose neurilemma studded with nuclei. Eventually they terminate, after the loss of this envelope, in the form of extremely fine still branching filaments. The latter measure less than 00023 mm. in diameter. At intervals in their course, as well as at the nodal points of their division, small structures like nuclei are to be observed. Betiform connections among the fibres appear to occur only as exceptions. In connection Avith other nerves, hoAvever, to Avhich a sensory nature may be ascribed with greater or less probability, terminal networks of various kinds, formed of pale fibres, have been described. Arnold the younger, for instance, mentions such an one on the surface of the con- junctival mucous membrane, and Billroth another on the mucous membrane of the pharynx of the water salamander. Again, Koelliker speaks of one in the mucous membrane of the small intestine of the frog, and confirms Billroth's statements as regards the pharynx of the last- mentioned animal. Similar terminal networks of pale fibres have also been described by Axmann and Ciaccio as occurring in the cutis of the frog, and, many years ago, as existing in the tail of the tadpole. Klein has also met with the same networks, and described them as occurring very Avidely throughout the body of the same animal. For many years past we have known of certain isolated instances of their occurrence in the skin of mammals, and Schbbl has recently demon- strated their presence here in great abundance. There can be no longer any doubt that the most superficial termina- tions of sensible nerves frequently penetrate into the epithelial layers of their organs. But their ultimate arrangement is still very A*ariously explained.^ The fact is, that at the present time our modes of investigation are still too imperfect to admit of our settling the matter conclusively. Some suppose them to end in a terminal plexus, so that Ave Avould only have an intermixture simply of epithelial cells and nerve fibres. Others, again, state that the latter penetrate into the cells and end in the nucleoli. Thirdly, many support the vieAv that there exist certain peculiar 332 MANUAL OF HISTOLOGY. structures imbedded in the epithelium, in which the nerve fibres ter- minate. These are known as Langerhans' cells. A feAV more points may be mentioned in regard to these views. A feAV years ago an excellent observer, Hensen, stated that in the tail of the tadpole the terminal filaments penetrated into the nucleoli of the epithelial cells. His observations gained greatly in interest through the further investigations of Frankenhauser and Arnold (§ 183). But these statements have not since been confirmed, and must now be declared incorrect: this we maintain against Lipmann, who asserts that very delicate nerve fibrillae may be seen to terminate in the nucleoli of the posterior epithelial cells of the cornea. We must also confess our disbelief in Joseph's theories with regard to a similar ending of the nerves in the cells of bone, and to Lavdowsky's with respect to those of the cornea. But, on the other hand, we have since learned from the beautiful inves- tigations of Hoyer and Cohnheim, that very fine nerve-fibres or primitive fibrillae do terminate in the epithelium of the corneal conjunctiva. Of this there can be no doubt. thelium* side branches, which ascend vertically in the epithelium, sending out twigs in various directions, and terminating as such in the superficial epithelial layers. The same arrange- ment almost is to be seen in the human cornea. According to Klein, tAvo very dense webs of the most delicate nerve fibres are to be found in the epithelium, a deep and a terminal, which is very superficial, only covered by about two layers of cells. In the year 1868 Langerhans pointed out fine non-medullated nerve fibres passing in between the cells of the rete Malpighii, partly uniting here with elongated oval cells measuring 0*0088-0*0033 mm., and partly pass- ing on farther upAvards Avith subdivision. This arrangement Avas con- firmed as existing in the cornea of the rabbit by Podcopaew. A similar arrangement of terminal nerve filaments had, however, been found before this in the mucous membrane of the tongue by Freyfeldi- Szabadfoldy ; and Luschka made the same discovery in regard to the lining TISSUES OF THE BODY. 333 membrane of the human larynx. Kisseleff appears to have seen simdar things in the mucous membrane of the frog's bladder, and recent investiga- tions by Morano, Klein, Elin, and Chrschtschonovitsch, show that the same arrangement of non-medullated filaments exists in the epithelium of the conjunctiva, mouth, and of the vagina, sometimes with, sometimes with- out the corpuscles of Langerhans. The mode of termination of the nerves in the pulp of the teeth (already mentioned, p. 269), has also been recently followed up. Nervous twigs have long been known to exist in the walls of this struc- ture. They may be easily seen here, and consist of dark-bordered fibres whose diameter is 0-0038-0*0067 mm. These run upwards parallel to each other, and then form an elongated nervous network by the branching of their fasciculi. By the binary subdivision of these nervous twigs immense numbers of very delicate silky primitive fibrillae are formed, according to Boll, Avhich resemble elastic fibres in some degree, but which are never seen to join in a reticulated manner. These pass in between the odontoblasts (p. 270) to reach the inner surface of the dentine, where they probably sink into the dental canaliculi. Thus the latter contain a double system of fibres, composed partly of Tomes' dental fibres (p. 270), and partly of these nerve fibres. The well-known sensitiveness of the tooth depends upon the latter. § 188. We now turn to one of the most difficult subjects in nervous histology, and one which is still the theme of much controversy—namely, the struc- ture of the ganglia. In regard to the relation of the nerve fibres to the cells even in the bodie3 of fishes, where research is attended with least difficulty, considerable differ- ence of opinion still exists. But this is the case to a far greater extent in man and the higher vertebrates, where the difficulty of obtaining good and serviceable objects is very great. Besides, it would be hardly prudent to make use here of analogy to too great an extent, and to apply those discoveries, which have been made in the body of the fish, to the human organisation Avithout due caution,—in that Ave are not able to estimate, with any certainty, the whole physiological connection between nerve fibres and cells in general. On the other hand, it is no less dangerous to take isolated observations, which have been with difficulty made on the human and mammal body, and, generalising from these, to dash off with bold strokes plans of the organisation of the nervous knots, which dazzle us for a time by an apparent physiological consistency, it is true, but Avhich may be subsequently recognised as entirely incorrect. At first sight we recognise investing the nervous ganglia an envelope of connective-tissue of varying thickness, a modified perineurium, consisting partly of fibrillated connective-tissue alone, and partly of the latter inter- mixed with Remak's fibres. This fibrous mass, in which the blood-vessels of the ganglion are situated, extends also into the interior of the organ, Avhich is, however, chiefly made up of ganglion cells packed closely together. The nervous trunk or trunks entering the knot (fig. 319, b) are divided in the latter into fasciculi, Avhich conduct themselves in various ways. Some of them, namely, traverse the structure directly, or with but little deviation from the straight line (k), Avhde others are resolved into primi- tive fibrillae (I), which continue their course through the ganglion, twist- 334 MANUAL OF HISTOLOGY. ing and winding in every possible direction between the cells of the latter. Eventually, however, they become again united into bundles, Avhich asso- ciate themselves with those which passed through in a straight line. In this way are formed the stem or stems which leave the ganglion (d, e). The nerve fibres entering the knots have, on this account, been classed into " direct" and " tortuous," terms which will still be found appropriate. There exist, however, as might be supposed, many intermediate forms between the tAvo modes of arrangement. It used formerty to be believed that the relation of the fibres to the cells within the ganglion was only that simply of close proximity. This view, hoAvever, was found to satisfy the requirements of the physiologist just as little as that Avhich held that the nerve-fibres ended in loops, and was finally abandoned on the discovery of the origin of the fibres. Confining ourselves for the present to the spinal ganglia (fig. 319), we find that a number of investigators have observed an extraordinary arrangement in these structures in the fish, namely, that all the nervous fibres of the posterior root of the ganglion are interrupted in their course Avithin the latter by a cell,—the broader fibres usually by a larger, the finer by a smaller element. The corresponding ganglia of mam- mals and man, however, present but rarely such bipolar cells (h). Here some of the processes may take an op- posite'course, as in the fish, or both pass out beloAv towards the periphery (g). As a rule, we meet with nerve cells here which only give off one process towards the'cir- cumference (/), which may subsequent- ly divide into two fibres, according to Remak. Finally (and it is in the spinal ganglia of the smaller mammalian animals that we obtain the most characteristic objects), isolated apolar cells are to be found (i), probably but undeveloped forms of the first kinds. It appears, neverthe- less, undeniable that a certain number of the nerve-tubes entering the spinal gan- glia may pass through the latter without being connected in the least with its cells. Hoav many do so is not yet deter- mined. The ganglion cells found in the sympathetic knots (fig. 320, d, e f) appear to be somewhat smaller as a rule, but not so much so that we should feel ourselves justified in placing a distinction between sympathetic cells and cerebrospinal on this account. Fig. 319—A spinal ganglion from the mammal c (diagrammatic), a, anterior or motor, 6, posterior or sensitive root; d, e, efferent nervous trunk; *, direct, and l, tortuous fibres; / unipolar, g and h, bipolar, and i, apolar ganglion cells. The nervous fibres are some of them broad, but for the most part fine there may be seen in the sympathetic erable quantity, those formations known as Remak's fibres Finally, turning to the relation of the two kinds of structural element TISSUES OF THE BODY. 335 Fig. 320.—Sketch of a mammalian sympathetic ganglion, a, b, c, nervous trunks'; d, multi- polar cells; d*, some of the latter with a divid- ing nerve fibre; «,unipolar, and/, apolar cells. to one another,—in the first place, apolar ganglion cells (/) are to be met with, but Avhether their number is a large one or no, we are unable to determine. Secondly, unipolar cells (e) are encountered, giving off a deli- cate nerve fibre, which is distributed peripherally. Again, we meet with bipolar ganglion corpuscles, whose two nerve tubes take a course at one time opposed to each other, at another in the same direction. It is one of the many things also for which Ave are indebted to Remak, that he has pointed out besides, the existence in the sympathetic of a fourth form among these elements, namely, the multipolar cell. Taking their rise from the latter (d), we see from three to twelve processes Avhich, by rapid ramification, may soon in- crease threefold (d*). The amount of these is dependent on the number of nervous trunks in connection Avith the sympathetic knot, and into which the processes are continued in the form of nerve tubes : thus it is greater in the solar plexus than in the ganglia of other parts of the cord. According to the observer just mentioned, the processes of unipolar and bipolar cells of sympathetic ganglia undergo division likewise. §189. Beside these larger ganglia just described, Ave have to consider a multi- tude of smaller, and also most minute nervous knots, which have only recently been recognised, owing to their frequently microscopical dimen- sions. We find them, on the one hand, containing numerous ganglion corpuscles, or, again, with but few of the latter. Their number is quite surprising throughout the body. They seem to belong, more or less, to the sympathetic system, supplying principally the smooth and involuntary muscles Avith their fibres. Among these may be numbered groups of ganglion cells, which are found in the ciliary muscle of the eye, on the branches of the circular plexus to be found in the same (C. Krause, H. Muller). Several small twigs from the ciliary nerves, likewise penetrating into the choroid coat, form there, in the deeper portions of the latter, a delicate plexus, in which scattered ganglion cells and small aggregations of the same have been remarked (H. Muller and Schweigger, Sdmish). Other small nervous knots were discovered also, many years ago, by Remak on the branches of the iV. glossophanjngeus, distributed to the pharnyx and tongue; but those on the twigs of the Lingualis, supplying the last-named organ, are still more minute. The nervous twigs, likewise distributed to the walls of the larynx and bronchi, as Avell as the interior of the lungs, bear also similar ganglia upon them. Another series of extraordinary ganglia is to be met Avith in the muscle of the heart, presenting itself in man and the mammalia imbedded in the sub- 336 MANUAL OF HISTOLOGY. Fig. 321.—A ganglion from the submucosa of the small intestine of a suckling ten days old. a, ganglion; b, nervous twigs given off by the latter; e, injected capil- lary network. This preparation had been macerated for a very long period in pyroligneous acid. stance of both ventricles and auricles (Remak). The most carefully studied have been those of the frog, where they are situated in the septum between the auricles, and at the union of the latter with the ven- tricles. They are said only to contain unipolar cells. These ganglionic plexuses are also encountered in great abundance in the walls of the alimentary canal. Here at- tention Avas first directed to them by a discovery of Meiss- ner's, which initiated a series of further investigations. The first of these gangli- onic and nervous plexuses extends in the human and mammalian intestine from the stomach downwards through the submucosa. Its peripheral branches probably contain, for the most part, motor elements for the mus- cularis mucosa; and some few sensible fibres for the mucous membrane. This submucous ganglion plexus, as seen in the infant (figs. 326 and 322, 1), has narrow meshes, but in the adult broader and more irregular ones. The number of twigs given off from it is variable (fig. 321, b), and the ganglia differ also greatly as to size and shape (fig. 321, a; 322, 1, a). The smaller cells ofthe latter are entangled in the meshes of a nuc- leated perineurium which clothes (fig. 321, b; 322, c) likeAvise the efferent trunks and commissures, consisting of fine pale nerve fibres (322, 2). These cells are said to be unipolar, apolar, and bipo- lar : multipolar do not appear to exist here. Internally, this gang- lion plexus gives off twigs to the muscular coat of u , , . . " , the alimentary canal. Here, between the circular and longitudinal layers of the latter, a second nervous apparatus, no less remarkable, is to be found—namely, the so- called plexus myentericus (fig. 323), for the discovery of which we are indebted to Auerbach. Beaching from the pylorus to the rectum, it is seen as a regular and Fig. 322.—1. A large ganglion from the small intestine of a suckling ten days old. a, ganglion with its cells; 6, c, efferent nervous trunks with pale nucleated fibres in a fresh state. 2 Small nervous twig of the same nature from a boy five years of age, showing three primitive fibres. After treatment with pyTohgneous acid. TISSUES OF THE BODY. 337 delicate interlacement of nerves, woven, as it were, round the intestinal tube (a), and having polyhedral meshes. At each nodal point in these there is always situated an aggregation of ganglion cells (b), sometimes large, sometimes small, but usually causing but a moderate thickening of the cord. Two adjacent ganglia, also, may be connected by means of a band formed of cells, beside which form the most characteristic examples of annular ganglia and commissures are also to be met with. Though liable to variation to a certain extent, according to the different species of animals, the whole formation is usually very much flattened everywhere. Here again we also meet with smaller ganglionic bodies, pale and very fine nerve fibres, and a nucleated perineurium, beside which apolar cells are to be observed, with others giving off two or three processes. From this plexus in question innumerable delicate nervous twigs are sent off to the circular and longitudinal muscular fibres of the alimentary canal, presiding over the peristaltic action of the latter. The genito-urinary apparatus, also, is no exception in the occurrence of such small nervous knots. Thus they have been seen by Remak in the Fig. 323.—From the small intestine of the Guinea pig (after Auerbach). a, nervous Inter- lacement ; 6, ganglia; c, lymphatic vessels. bladder of the pig, and in other mammals by Meissner. In the same organ of the frog they may be recognised Avith great ease also (Manz, Klebs.) In the corpora cavernosa of the male organ of generation these knots Avere found between the years 1830 and 1840 by /. Muller. They are also present in the nerves of the human and mammalian uterus, and in the connective-tissue around the vagina, as well as in the submucosa of the latter. Remak and Manz mention ganglionic plexuses around the muscular gland-ducts of birds also. In the lachrymal and salivary glands of mammals, finally,—therefore, in organs Avhich elaborate large quantities of secretion under nervous stimulus, very complicated nervous networks of dark-edged fibres, richly studded with ganglia, have been met with by Krause. 338 MANUAL OF HISTOLOGY. §190. Of the chemistry of nervous tissue, but little is known on account of its anatomical peculiarities; for, in the first place, the most massive nervous apparatus, namely, the cerebro-spinal, which is on account of its bulk most frequently the object of chemical research, has a very complex struc- ture, and in it together Avith a ground-Avork of connective-tissue, we have to deal with nerve tubes and ganglion cells which cannot be separated. On the other hand, but little has been done to elucidate the nature of the albuminous substances of the neural apparatus, and much obscurity still hangs over the so-called cerebral matters (§ 20). The living nerAre displays, while at rest, a neutral reaction which be- comes acid at death. The same change is produced, also, according to Funke, by over excitement of the fibre. This is but a repetition of Avhat takes place in muscle under similar circumstances (§ 170). From the anatomical study of the various parts of ganglion cells, we knoAV that the latter are made up of albuminous compounds, in which fatty molecules and granules of pigment may be present (§ 178). We have seen likewise (p. 307) that the sheaths of nerve fibres consist of a substance resembling elastin, but more soluble than the latter in alkalies, whilst the axis cylinder is composed essentially of several matters belonging to the protein group, and the medullary sheath principally of cerebrin. All that is known of the chemical composition of nervous tissue has been learnt almost exclusively from examination of the substance of the brain. The specific gravity of nervous trunks is 1 *031, according to the obser- vations of Krause and Fischer ; that of the white matter of the cerebel- lum 1*032, of the cerebrum 1*036, and of the spinal cord T023, Avhilst for the grey substance of both cerebrum and cerebellum Ave find T031, and for that of the cord 1038. From several experiments which have been made, it Avould appear that cerebral substance possesses in a high degree the power of absorbing water. The amount of the latter in nervous tissue is subject to much variation. In some cases it is but moderate, and in others it may become very con- siderable. The proportion of water, for instance, in the peripheral nerves is estimated by Schlossberger at 70-78, or even 80 per cent., that in the Avhite substance of the brain at betAveen 69*64-70*68, and in the grey matter 84*84-86*64, showing that the latter is richer in aqueous consti- tuents. In the infant the brain is still poorer in solids. In the spinal cord the percentage of Avater is loAver, being, according to Bibra, 66 per cent. Of course this Avater is distributed over both the tissue and the nutritive fluids saturating the latter. As already mentioned, nervous matter consists of several albuminous bodies of cerebral substances (lecithin and cerebrin), together Avith mineral constituents. Finally, it contains certain decomposition products. Touching the albuminous matters, we are here more than elsewhere in the dark as regards their nature. Our slight unacquaintance Avith the chemical constitution of nerve cells only permits of our accepting the presence of one or more members of the group in general, but gives no indication as to Avhat substance or substances occur specially. The reactions of the axis cylinder are those of an albuminoid substance in a coagulated condition. But how far other albuminous matters may TISSUES OF THE BODY. 339 occur in nervous tissue, apart from a small amount of it in a soluble form, is still uncertain. Quantitively it is impossible to analyse them on account of being obliged to include the primitive sheath, and other tissue elements. The amount, besides, of residue insoluble in ether varies considerably, from 9 to 14 per cent. As soluble in ether, Ave obtain further the so-called cerebral substances lecithin and cerebrin (§ 20), and likewise cholestearin in considerable quantity (§ 21). The amount of these matters, further, has been found to be far greater in the white substance of the brain than in the grey, and they may, therefore, be regarded as essentially constituents of the nervous medulla, although we do not possess any satisfactory explana- tion of the manner in which they occur here being insoluble in Avater. From the fact that lecithin (which exists in great quantity in the brain), yields, besides neurin (§ 33), and glycerophosphoric acid (§ 16), palmi- tinic and oleic acid also, we may infer that the fatty acids and fats, upon Avhich such stress used formerly to be laid, were possibly only products of the decomposition of the former. Cholestearin, which occurs in cerebral tissue in large quantities (amount- ing, according to Von Bibra, to a third of the matters soluble in ether), has the nature likewise of a decomposition product. Turning now to the quantity of these matters soluble in ether, we find their proportion in the grey substance, in Avhich much Avater is contained, to be 5-7 per cent.; in the white tissue, which is poorer in the latter, on the other hand, it is 15-17 per cent., and rises still higher in the spinal cord. Considerable difference may be observed, also, between the various parts of the same brain. In the infant the amount of these matters is very small, there being, besides, no difference in this respect between the white and grey tissue. In the foetus they are present in still smaller quantity. Among the products of transformative processes going on in nervous tissue, may be reckoned formic and lactic acid (found in the brain), and possibly also acetic acid, also inosit, kreatin, leucin (in the ox), xanthin and hypoxanthin (Scherer), urea (in the dog), and uric acid. The ash of cerebral substance amounts, according to Breed, to 0 027 per cent, of the fresh tissue. In a hundred parts of the former he found :— Free phosphoric acid, Phosphate of potassium, . „ of sodium, „ of iron, . „ of calcium, „ of magnesium, Chloride of sodium, Sulphate of potassium, Silica, .... The preponderance of potash and magnesia over soda and lime recalls to mind the state of things in muscle. §191. Turning now to the application to neural physiology of the points regarding the structure of the nervous apparatus, which have just been described, we see in the first place, in the tAvo kinds of structural elements, a contrast between merely conducting fibres and cells which are endowed 9*15 55*24 22*93 1-23 1*62 3*40 4*74 1*64 0*42 340 MANUAL OF HISTOLOGY. with higher functions, Avith those of perception, and of directing voluntary and reflected motion. Thus we find the latter structures in the grey matter of the brain, spinal cord, and ganglia, to which Ave have long been compelled by experience to ascribe reflex functions. They are met with, also, at some other points where their significance is not yet quite appa- rent, as, for instance, among the terminal ramifications of some of the higher nerves of sense. With regard to the nerve tubes, we have learned from the last section that their varieties of form and thickness do not go hand and hand with functional differences. Thus the sensitive roots of the spinal nerves con- tain fibres which differ in no respect from those of the motor roots. In the sympathetic system Ave meet Avith Remak's fibres, whose nervous nature Avould seem to be almost beyond doubt, and to these the most analogous formations are the nerve tubes of the olfactory nerve. The fine medullated nervous fibres can with as little right be looked upon as a special sympathetic form, presiding over peculiar functions, as Avas formerly maintained by Volkmann and Bidder; for numbers of inter- mediate grades between coarse and fine tubes are met Avith at points where there can be no suspicion of sympathetic influence. In this respect the accurate microscopical analyses of recent times has greatly modified the sanguine expectations of an earlier epoch. On the other hand, some important aids to physiology have been acquired through the knowledge of the finer anatomy of the nerve fibre. All observers concur in regarding the continuity of the nerve tube as certain,—a point necessardy accepted as indispensable by the physiolo- gist, likewise in respect to the isolated course of the latter. Thus we see everywhere the same state of things; the nerve fibre taking an unin- terrupted course through the long interval between the nervous centre and the place of its final termination, although this course may be modified somewhat by the insertion of a ganglion cell. The question as to what part of the nerve tube is to be looked upon as the really active, i.e., conducting medium, may perhaps be answered in favour of the axis cylinder, in that it is frequently the only portion present at the origin of the nerve fibre, and probably always at its ultimate termination, whdst the medullary and primitive sheath enclosing it are here absent. At those contracted portions of the fibre, also, which are seen at points where branches are given off, the axis cylinder may present itself for a short distance divested of its usual medullary envelope. The theory of the termination of the nerves in loops having been shown to be incorrect, has given further support anatomically to the theory of isolated conduc- tion. The separate termination of the nerve fibre, whether single or Avith many ramifications, is also consistent Avith the vieAvs of the physiologists of the present day. The splitting up by which, as we have seen in the nerves supplying muscle, a primitive fibre may become resolved into a multitude of branches, must be looked upon as an ingenious provision of nature for obtaining as highly nervous a periphery as possible, both sensi- tive and motor, with comparatively thin nervous trunks. This arrange- ment seems certainly to have the character of something belonging to a lower order of creation, for the higher we ascend in the animal kingdom, the more do the numbers of tubes and muscle fibres become alike, as we have already remarked above. An acquaintance Avith the terminal appa- ratus of motor nerves is, also, another important advance recently made. Regarded from a physiological aspect, Krause's and Kuhne's discovery of TISSUES OF THE BODY. 341 muscular substance, excitable though free of nerves, has done much towards the adjustment of that very old controversy in regard to whether there be such a thing as muscular irritability. The termination of sensory nerves in special anatomical structures, such as the Pacinian bodies, or Krause's tactde corpuscles, is also of great interest. To return to the ganglion cells : there seems to be among them just as little coincidence between their anatomical variety and physiological difference as among the nerve tubes. The physiological significance, further, of the apolar nervous cells, is still unknown to us; even the fact of their existence has in it something strange to the physiologist. The unipolar cell, also, which is looked upon as the starting-point of the fibre proceeding from it, should be connected with the cells adjacent to it by commissures. The physiological purpose for which bipolar cells exist is likewise veiled in obscurity. The most comprehensible are the multi- polar elements with their efferent nervous fibres. But, although we are at present unable to understand many things in the texture of the ganglion, nevertheless, important points in relation to the motions of organs have been gained by an acquaintance with the smaller ganglionic plexuses discovered in such surprising numbers. We refer to the submucous ganglionic networks, and plexus myentericus of the digestive apparatus. Living nervous substance, further, has, like muscle, electromotor pro- perties. As to the amount of interchange of matter which goes on in the nervous elements, we are still in the dark. That it is probably consider- able, is indicated by the fact that a fatigued nerve regains, after a certain period of rest, its original power of functionating, and also that ligature of the arteries of a part brings about a rapid paralysis of the motor and sensible nerves supplying the same. The scanty notes of the preceding section likewise contain all that is at present known of the nature of this interchange of matter. As to the question, further, how far an anatomical ohange goes hand in hand with the chemical, or, in other words, how far the nerve tubes and cells may be regarded as persistent structures, or, on the other hand, only destined for a short existence as transitory formations, we are unable to give any answer. The corpuscles and fibres present themselves in far too great variety of form in the adult body for us to be able to separate young, mature, and older elements from one another. § 192. The mode of development of nervous tissue in the embryo is one of the most obscure chapters of modern histology. That the brain and spinal cord, together with the internal portions of the higher organs of sense, formed from the first of these, are productions of the so-called corneous layer of Remak, is an ascertained fact. They take their rise, in other Avords, from the cells of the upper cellular layer nearest the embryonic axis. On the other hand, the point of origin of the ganglia and peripheral nerves is still unknown to us. We are still unable to determine whether, as is very probable, these parts are productions of the corneous embryonic leaf, or whether, according to one view which is held, they have not originated independently in the middle germinal plate, and only become subsequently connected with the nervous centres. The connection of 342 MANUAL OF HISTOLOGY. the ends of nerves with tissues at the periphery, such as the muscle fibres which, as far as we know at present, have had their origin from the middle germinal plate, is a great theoretical difficulty. The usual but unsatisfactory vieAv Avhich is held regarding ganglion corpuscles is that they are metamorphosed formative cells. By the enlargement of these, and their subsequent acquisition of a characteristic finely granular contents, the ganglion cell is arrived at. When their further growth takes place regularly we have the apolar element, and the structure Avith processes when the former is unequal. Through these latter adjacent cells may be connected, and from them nerve fibres are given off. It is possible that multiplication by segmen- tation may take place in already formed nerve cells in the foetal body, but the subject requires closer investigation. The formation of nerve fibres, which has been already touched on in the general part of our work (p. 100), Avas formerly supposed generally to be brought about by the fusion of ceils in such a way that (in the case of the non-ramifying nerve tube) connection took place betAveen the indivi- duals of a series of fusiform or cylindrical elements. The nervous trunks of man and the mammalia have not that white appearance in early foetal life Avhich characterises them at a later date; they are on the contrary grey and translucent, the more so the younger the embryo. ' At first we only remark on teazing them out the individual formative cells of fusiform, or simply elon- gated figure, and with vesicular nuclei. Later on we may suc- ceed in splitting off rows of these from the main structure in the form of pale fine nucleated bands. These are the first nerve fibres whose pale non-medul- lated appearance reminds us of Remak's elements; their me- dium breadth is 0*0029-0*0056 mm. In the older nerves we may perceive the specific contents of the primitive tubes, advancing gradually from the central to- wards the peripheral portions, the axis cylinder arising in all probability first, and the fatty medullary mass being deposited subsequently betAveen it, and the primitive sheath formed of the membranes of the cells. These, then, are the usual views on the subject based upon Schwann's outlines, which have Fig. 324.—Development of nerve fibres; from the tail of a tadpole. 1. A pale still non-medullated fibre with two nuclei. 2. More advanced tubes parUy filled with medullary matter, a, a fibre, with which =» stellate formative ceU (a>) is connected at its side, more developed, at a, the stem at 6, and c, the branches. been received into histology. The formation of branches on nerve fibres was supposed to take place TISSUES OF THE BODY. 343 by the fusion of stellate formative cells (provided usually Avith three processes), Avith the terminating portion of the already formed fibres, the latter growing by the addition at their periphery of new cells. The tail of the tadpole and electric organ of the torpedo Avere put forward as suitable objects for the recognition of these points. And, indeed, here we have the best opportunity at this great distance from the central organs of coming upon younger and younger specimens of nervous branches. In the tail of the tadpole (fig. 324) we encounter isolated nerve tubes, Avhich bear all the characters of Remak's fibres, showing nuclei situated one behind the other (1). Others (2 b) Avithout any thickened envelope appear dark and medullated in the upper part, Avhile below they become finer, and are continuous with the peripheral formative cells (bl b2), which radiate Avith their pointed processes in the surrounding tissues. Again Ave may meet, and by no means uufrequently, with nerve fibres possessing thickened envelopes (2 a) and dark medulla, which is con- tinued below into a progressively paling fibre (2 a3 and «4) resembling an axis cylinder. Xow, although we do not yet possess a satisfactory knowledge on these points, nevertheless Ave have acquired enough material to demonstrate the untenableness of these earlier views. Bidder and Kupffer, in their inquiries into the origin of the spinal cord, found that the formation of nerve tubes from one row of cells occurs neither in the Avhite substance of the organ, nor in the roots of the spinal nerves. In place of these fibrillae only are observed, without nuclei and cells. These, the axis cylinders of the future, according to the authors in question, grow simply outwards towards the periphery. The envelopes appear to be formed for themselves subsequently, from new tissue elements appearing between these fibrillae. The late excellent observer Remak also maintained, many years ago, quite a different mode of origin for the ramifications of nerves in the tail of the tadpole from that described in the text. According to him, the branching rudiments of the cutaneous nerves appear everywhere to be prolongations from the spinal ganglion. According to Hensen, also, the nervous ramifications in this well- trodden locality are present from the commencement all the Avay down to the periphery, in the form of fine, lustrous forked.fibres (axis cylinders) with- out a sign of nuclei. It is only subsequently that the mode in which they become sheathed in thin, pale, and extremely elongated cells, can be recog- nised, until eventually the axis cylinder lies in the interior of a nucleated envelope, the stellate cells spoken of taking no part in the process. Besides a great instabdity in their contents, OAving to Avhich the latter may assume the appearance of a chain of separate drops, the newly-formed nerve tubes are remarkable for their great fineness as contrasted with corresponding elements in the mature body. The increase in thickness of the Avhole nervous trunk is sufficiently explained by the augmentation in the diameter of the individual primitive fibres. According to Harting, their thickness in the median nerve of a foetus at four months is only 00024 mm., while in the infant and adult they measure respectively, on an average, 0*0103 and 0*0164 mm. The number of primitive tubes, at these three periods, were estimated by him at 21*432, 20*906, 22*560. It is a Avell-known fact that nerves, on being severed, cease to fulfil their functions, but after a certain time has elapsed regain their powers. The separated ends, namely, heal rapidly; yes, and even after a tolerably 23 344 MANUAL OF HISTOLOGY. long piece has been cut out from a nervous trunk, connection is again restored by means of new tissue. According to the early observations of Waller, which have been since con- firmed by others, that part of the nerve situated at the distal side of the cut degenerates doAvn to its ultimate ramifications, with coagulation and subsequent absorption, until eventually the neurilemma alone remains, which also disappears completely after a certain time, according to the same investigator. From this we infer that a new formation of nervous fibres must take place in order to effect connection with the central por- tion. This last view is opposed by Lent, who asserts that a new filling-in of medullary matter into the primitive sheath supervenes upon the union of the tAvo cut ends. According to Hjelt, finally the severed nerve fibres only degenerate in part completely, being replaced by neoplasis, Avhilst other primitive tubes are capable of a regeneration subsequent to their reunion. Lent, again, has observed a very interesting multiplication of nuclei in the primitive sheath. But the whole question, as regards the origin of the newly-formed interposed tissue, is Avorthy of being made the subject of renewed research in the present state of histology. Whether regeneration of ganglion cells takes place is still uncertain. Pathological new formation of nervous elements in other neoplasms is of rare occurrence, as are also nervous tumours or neuromas. The latter may consist of tubes or grey matter In atrophied nerves a decrease in the thickness of the primitive tubes is manifest, and, instead of a continuous medulla, a number of fat globules and granules are presented to us. 16. Glandular-Tissue. § 193. The definition of what we understand by a gland was, until compara- tively recently, a matter of considerable difficulty, so that a talented anatomist, more than thirty years ago, Avas fully justified in expressing Fig. 325.—Glands from the large intestine of the rabbit. A fol- licle filled with gland cells; four others without cells, show- ing the membrana propria. Fig. 32G.—A racemose so-called mucous gland from the rab- bit's oesophagus. «, the duct; b, the follicles; c, the invest- ing connective tissue. himself thus:—" That class of structures called glands is one of those careless productions of an infant science, to define which, set it upon a firm basis, and support it there, requires all the care and pains Avhich the latter can bestoAv in its present state of maturity." TISSUES OF THE BODY 345 In the earlier days of anatomical study a round form, soft consistence, and great vascularity, sufficed to gain for an organ the name of " gland." Later on, hoAvever, the physiological requisites for the proper conception of a gland became more prominent. And first of aU, that the latter abstract from the blood matters which are not to be made use of for its OAvn nutrition, but which tend to benefit the Avhole system, either by being cast out of the body as decomposed material to be gotten rid of, or turned to account in the economy as specially prepared by the "land. Thus, the latter came to be looked upon as a secreting organ, great stress being laid, consequently, on its efferent duct. Finally, it was recognised that there are many completely closed organs from Avhich no secretion is ever given off, and to which, nevertheless, we cannot deny the right to be called glandular structures. This was subsequent to comparative anatomy having shown the comparatively small weight to be given to the duct as the distinguishing mark of glands. Recent microscopical analysis has supplied us with characteristic signs by Avhich, in general, a gland may be diag- nosed, although there remain certain points relating to structure about Avhich doubt still exists. The history of development like- wise has also afforded most important information here. From it we learn that the physiologically important parts of true glands, namely, their secreting cells, all take origin either from the corneous or intestino-glandular em- bryonic leaves. No truly glandular organs spring from the middle germinal plate. Finally, owing to our extended knowledge of the nature of the lym- phatic apparatus, Ave are now enabled to class Avith the latter as lymphoid organs a series of parts springing from the middle embryonic leaf, which used formerly to be reckoned among the glands. Let us now return to the histogical characters of glands. These organs consist of tAvo kinds of structural elements (figs. 325and326)(l)ofafine structureless transparent mem- brane,\i.no\vn as the membrana propria, Avhich determines the form of the organ as well as that of its sub-divisions, and (2) of the contents * of the latter, the so-called gland cells (figs. 325, 327. and 328). As a third indispensable factor, we find on the external surface of the homogeneous membrane a vascular network (fig. Fig. 327.—Gastric glands from the dog, filled with cells, and interlaced by a vascular net- work. Fig. 328.—Lobule from the liver of a boy ten years old. 346 MANUAL OF HISTOLOGY. 327), from the contents of which the materials of the secretion of our organ are abstracted. Of the three requisites of a gland the blood-vessels and cells are never absent, and the homogeneous membrane only rarely so. Besides these, Ave have to take into account the nerves distributed to the organ, the lymphatics, connective-tissue, and at times also muscular en\*elopes ; and, finally, as a frequent occurrence, a special and often toler- ably complicated excretory duct. § 194. The membrana propria, when such a structure exists, presents itself in the form of a homogeneous envelope, at one time immeasurably thin, at another thickened frequently up to 00011, or more rarely 0*0023 mm. It is often mixed with or enveloped in an extra layer of connective-tissue until a tunic of 0*0045-0*0090 mm. results. As an exception, Ave may perceive betAveen these two strata a layer of unstriped muscle, as in the large sweat glands of the axilla. At times, also, as, for instance, in the sebaceous glands, Ave find the membrana pro- pria replaced by an undeveloped connective-tissue. In other cases there appears (fig. 329) imbedded in it a web of flattened connective-tissue cells contain- ing nuclei (parotid, submaxillary, and lachrymal gland). The structureless membrana propria manifests further a considerable amount of distensibility and strength, and likeAvise of power of resistance to the action of weak alkaline solutions and acids, so that these may be made use of with good effect for its demonstration. At present Ave are not acquainted with its chemical constitution ■ it is probably formed in many cases of some substance closely allied to elastin. From an anatomical point of vieAv, this covering * may be regarded as determining the form of the organ as already mentioned, physiologically it serves for the filtration and transudation of the plasma. In respect to the histology of the structure, it has been supposed to be a substratum secreted by the first aggregations of rudimentary gland cells on their exterior, and hardened in that situation. This process was looked upon as having taken place at an early period in existence, the membrane out- living many generations of gland cells. But another recent view appears to us far more Avorthy of acceptation, namely, that the gland-membrane is only the transformed, and more or less independent limiting layer of the surrounding connective-tissue, and represents therefore a contiguous por- tion of the middle germinal plate. This theory offers an easy explana- tion for the presence or absence of the membrana propria. It seems, moreover, to be a characteristic of the gland cells, in contradistinction to other cellular elements of the body, that they do not generate externally definite formed products. The shapes under which the membrana propria or limiting layer of con- nective-tissue presents itself to us, are, as has been already remarked very various. Three varieties may be generally recognised, and corres- Fig. 329. — AVeb of fiat stellate connective-tis- sue cells isolated by maceration from the membrana propria. From the submaxillai-y gland of the dog, after Boll. TISSUES OF THE BODY. 347 ponding to these, three forms of glands, which are, however, here and Fig. 330.—Simple tubular glands from tlie mucous membrane of the human stomach. Fig. 331.—A convoluted gland . from the con- junctiva of the calf. Fig. 332.—Tlie vesicles of a racemose gland (Brun- ner's) from the human being. there blended one into another, and also make their appearance at one time as simple, at another as very complex apparatuses. (1.) In the first form (fig. 330) the envelope presents itself as a narroAv passage of very variable length, almost ahvays closed at one end and open at the other, discharging itself either indepen- dently or in connection with other structures of the like nature in the form of a very complex apparatus. An envelope of this kind is known as a gland tubule, and such glands are named tubular. Of these two kinds are recognised, namely, the simple, where the whole organ con- sists entirely of one microscopically small, sac ; and the complex, Avhere several or very many of these tubuli are combined to form a new anato- mical unit, or if Ave prefer another view, Avhere the tubules are sub-divided. They may even form a retiform combination of tubes. If the latter attain great length, as is the case in two com- pound glands of the human body, the testicle and the kidney, they may be regarded as a special variety under the name of gland tubes (fig. 333, a-e). Branching urni- ferous tube from the kidney of a kitten, a-e, progressive subdivision at acute angles. 348 MANUAL OF HISTOLOGY. Fig. 334.—One of Brunner's racemose glands from the human being. Another peculiar species of tubular glands is presented in those in Avhich the upper and 0^ usually undivided blind end is tAvisted into a con- volution like a coil of rope (fig. 331). To these the suitable name of " convoluted glands " has been given (Knauel- driisen of Meissner). (2.) In a second group of glandular organs we meet the membrana pro- pria under the elementary form of the so-called open gland vesicle, that is of a short wide blind sac of microscopic dimensions (fig. 332). This struc- ture may frequently be very aptly compared to a short-necked flask Avith a Avide body, Avhilst in other cases it is more like a spheroidal berry or short blind gut. In this case the most characteristic points are the grouping of these vesicles together. Such a group (which frequently attains considerable dimensions) may form a complex gland still of microscopical minuteness, or may be associated with other aggregations as a sub-division of an organ (figs. 326 and 334). These aggregations are knoAvn under the names of lobuli or acini (1). From these open vesicles a multitude of glands is built up, as, for instance, the so-called racemose, which, with all their variety of general figure and difference of size are really under the microscope, comparatively speaking, very uniform as to structure. No very sharp line, however, can be drawn between these last described and the tubular species. If the walls of the latter be not smooth, namely, and the membrana propria bulges outwards in the form of spheroidal projections, and that a certain division of the sac is combined Avith this, we have as a consequence inter- mediate forms which may Avith equal right be said to belong to either species of gland. (3.) In a third species of glands we find a bounding layer of connective- tissue in the form of a roundish capsule, closed on all sides, and fre- quently of considerable size (fig. 335). Capsules of this kind get rid of their contents either by rupture of their walls, known as dehiscence, by Fig. 335.—Glandular capsules from the thyroid of a child. a, ground-work of connective-tissue; b, the capsule itself; c, gland cells of the latter. TISSUES OF THE BODY. 349 which they are, without exception, destroyed, or the cavity remains closed during the whole of life, the contents exuding through the parietes. To the first of these species the glandular elements of the ovaries belong; to the second, those of the thyroid body. In man, hoAvever, we never meet with a whole gland formed of one closed capsule by itself, as is the case with the tubular follicles. The few organs in our body which may be numbered with the last species, are composed of a multitude of elements of this kind imbedded in a connective-tissue ground- Avork. Remarks.—The word "acinus " is also made use of to designate the gland-vesicle, so that it is a3 well, perhaps, to avoid the term entirely. §195. The second, and more important elementary structures of the organs Avith which we are noAv engaged, are the gland cells. These are derived from the corneous and intestinal glandular embryonic lea\*es, and in keeping with their origin, never completely lose their epithelial characters. In the bodies of many of the loAver animals the significance of these gland cells appears in the most striking way. The interesting discovery, namely, has been made, that in them there exist glandular organs Avhich consist of but one single cell only. Within the cavities of glandular organs these cells are either packed closely together Avithout order, filling out the former, or they clothe their internal surfaces like epithelium. Xot unfrequently, when so arranged, their figure is polyhedral. They may also occur either arranged in one single layer, or forming a double lamina. At the outlets of glands these cells are continuous with those of the neighbouring epithelial formations, and frequently Avithout any sharp line of demarcation, so that the latter may be looked upon as having become gradually transformed into glandular elements. Indeed, Ave meet with Fig. 336.—Cells from the peptic glands of man. a, cell without a membrane; 6, a nucleus enveloped in a residue of the body of the cell; c, a cell with two nuclei; d-g, cells with sharper contour and decrease in the number of granules usually contained in such. many glandular organs whose cells are but little different, at least anato- mically, from those of the epithelia. # The different species of cells which are met with in the latter have their Fig. 337.—Human hepa- tic cells, a, one with a single nucleus; 6, another with two of the latter. 350 MANUAL OF HISTOLOGY. Fig. 338.—Transverse section through the mu- cous membrane of the small intestine of a rabbit (near the surface), a, reticular con- nective substance containing iymph cells; 6, lymph canal; c, transverse section of a follicle of Lieberkuhn; d, another of the latter with its cells in situ; e, /, g, blood-vessels. counterparts again ariong those lining glands. On account of the physio- logical calls made on them, however, they require greater volume than simple epithelial elements. For this ^fjfe/^t , reason Ave miss among them the ex- tremely flattened scales of many pavement epithelia, and meet, on the other hand, as a rule, more cubi- cal forms, which display, however, considerable diversity to the manner in which they are fitted in among their neighbours. Ciliated gland cells are never met with in the human body, if we except those of the gland-fol- licles of the uterus, and are but of rare occurrence elseAvhere. Deposits of melanin likewise are never seen here, although granules of yellow and brown pigment are not so rare. Small spheroidal or completely spherical cells, first of all are to be found for instance in the ovary, clothing its capsules and larger ones in the sebaceous glands of the skin and meibomian of the eyelids. The gland cell may frequently re- semble very closely, when seen from above, one of the elements of flattened epithelium, its body having become widened out. It is in this form that the cells lining the peptic glands of the stomach are presented to us (fig. 336), and also those of the liver (fig. 337), with many others. Another species is the more or less cylindrical cell. This is to be seen in the uterine glands, the so-called tubular mucous glands of the stomach, and racemose glands of mucous membranes (Schlemmer, Puky Akos, Schwalbe), and in Lieberkuhn's fol- licles of the small intestine (fig. 338, d). In the latter, according to Schulze, the most exquisite examples of "beaker cells" are to be seen between the ordinary columnar elements. We have recently been made acquainted Avith the fact that in certain glands there exist two Fig. 339—Gland capillaries from the pancreas of a rabbit, filled with Berlin blue (after Saviotti). 1 and 2, a large excretory duct; 6, that of an acinus; c, finest capillary passages; 3 an acinus with cells, and gland capillaries only partiaUy filled. TISSUES OF THE BODY. 351 kinds of cellular elements, as, for instance, in the submaxillary and peptic glands of many mammals. We shall refer to these again. Differences in gland cells have also been remarked corresponding to their conditions of activity and rest, e.g., in the glands of the stomach and submaxillary of many mammals, &c. Finally (en passant), betAveen the hepatic elements, and later still between those of several racemose glands, a system of the most delicate canals has been met with, to which the name of " gland capillaries " has been given. Fig. 339 will give some idea of the nature of these. Turning now to the size and further composition of the gland cell, we observe great diversity, especially in the former. Those elements, for instance, clothing the internal surface of the ovarian vesicles, possess a diameter of only 0*0074-0*0090 mm., while the roundish polyhedral cells of the racemose mucous glands measure 0 0068-0 0113 mm., those of the peptic glands 0*0226-0*0326 mm., and those of the liver almost as much, &c. In these cells are to be found single, or not unfrequently double, nuclei of from 0*0056 to 0*0090, at one time vesicular, and at another more homogeneous. At a later period, in the more mature cell, these may, how- ever, become dissolved. The contour of such elements is usually very deli- cate, and their contents are of various kinds; this we shall again refer to. §196. The delicate constitution of the cells in question, together with the lively interchange of matter which is carried on through their agency, tends to render the existence of a certain number of them very transitory, showing again another parallel Avith many epithelial elements. But while we are able to demonstrate the briefness of the existence of many cells with aU the certainty desirable, we have no facts to support us in other cases, nay, we even have observations which point to the very opposite conclusions as regards them. Thus the hepatic (fig. 337) and renal cells are knoAvn to be comparatively permanent elements. Here again, as among the epithelia, mechanical Avear and tear takes place also, the stream of fluid which flows toAvards the outlet of the gland carrying off Avith "it greater or smaller quantities of the cellular lining. If Ave observe, for instance, the stratum of mucus which covers the coats of the stomach Avhile digestion is going on, especially among phytophagous animals, we may frequently discover extraordinary numbers of peptic cells swept away in the gastric juice which wells up from below. The sebaceous secretions of the skin contain likewise cellular elements derived from the glands, from Avhence they emanate. In other organs, however, such as the kidney, lachrymal, and sweat glands, the cells appear to be washed away to a smaller extent, and in the bile hepatic cells are never to be found. The transient nature of these elements»is manifested again in another Avay. They are destroyed, namely, to form the secretion of the gland to Avhich they belong. Without taking into account such peculiar changes as lead to the origin of spermatozoa within the cells of the seminal tubules, we find the most ordinary mode of decay to be in physiological fatty degeneration, as it may be expressed, of the elements of glands. Here the cells are observed to be destroyed by the generation within them of fatty contents, undergoing subsequently a process of solution by which the latter are liberated, and appear as constituents of the glandular secretion. This is found to take place in the sebaceous glands 352 MANUAL OF HISTOLOGY. sebaceous of the skin, in the mamma during lactation, in the Meibomian and ceruminous glands, as Avell as many of the sudoriferous organs. Thus we see the saccules of sebaceous glands (fig. 340, A) clothed on their internal surface with cells (a), which may be regarded as a modified prolonga- tion of the Malpighian layer of the skin, but which differ from the latter in being to a certain extent rich in fatty granules (B, a). By a further deposit of fat Avithin the cell the latter is increased in size (B, b-f), and becomes detached from the membranapropria (A, b), so that in the cavities of the organ cells of 0*0377-0*0563 mm. are met with— elements in Avhich the amount of fat is very considerable. The latter presents itself either in the form of innumerable granules (B, b), or several globules of oil (c) enclosed within the membrane of the cell, or, one large drop communicates to the latter the appearance of an ordinary fat ced (d). The nuclei of these elements are gradually de- stroyed, apparently, as also their envelopes, at least frequently. Thus the secretion of sebaceous glands contains, in the first place, free fatty globules, and in the next place, those cells loaded with oily matters just described. A process precisely similar to this takes place in the mamma of the nursing woman. Here we see in the so-called colostrum (a milk which is secreted during the later period of pregnancy) round bodies of 0*0151-0*0563 mm. in diameter (fig. 341, b), know as colostrum corpuscles, Avhich are simply aggregations of fatty particles of together by some agglutinating matter. At one time possess envelopes and nuclei, at another to be Avithout either. There can be no doubt that in these structures are presented to us the gland cells which have been shed, and having undergone fatty degeneration, are now in process of solution. Soon after delivery the milk contains innumerable milk globules as they are called (a), that is, small drops of oil#enclosed in a delicate film of coagulated casein. These bodies are of very different diameters, measuring from 0*0029 to 0*0090 mm. In this case the increased energy of secretion has led to rupture of the gland cells Avhile still within the organ. In those situations where the gland cell possesses a finely granulai body consisting of albuminoid matters, we find it a matter of greater difficulty to convince ourselves of the destruction of the former in the formation of the secretion. We usually meet, however, in the mucous and peptic glands of the stomach with a certain number of liberated Fig. 340, gland, a, gland cells clothing the walls; b, those which have been cast off, filled with oil globules, and occu- pying the lumen of the sac; B, the cells under higher magnifying power; a, smaller specimens belong- ing to the parietal layer, and poor in fat; b, larger, with abundance of the latter; e, a cell in which several oil globules have coalesced to form larger drops; and d, one with a single fat globule; e, /, cells whose fat has partially escaped. varying size, held they are seen to Fig. 341. — Form ele- ments of human milk. a, milk globules; b, colostrum corpuscles. TISSUES OF THE BODY. 353 molecules, as well as naked nuclei, and even broken down cells, so that the destruction of numerous cellular masses cannot well be denied. Such cellular debris has long been known; at an earlier epoch, hoAvever, by reversing the order of things, a vieAv of its nature was taken Avhich favoured the theory of the spontaneous origin of cells. Another, and it appears equally widely-spread destructive process, is met with in the metamorphosis by which mucin is formed. Ordinary albumi- nous cells made up of the usual protoplasm occupy the parietal portion of the glandular sac, while larger elements containing mucus, and Avhich have had their rise in the first form, are situated in the more central part. By the solution of the latter the mucus of the gland is produced. This is found to take place, for instance, in numerous small mucous glands, such as the labial of man and the rabbit, those of the larynx of the latter animal and the dog, in the submaxillaris of many mammalia, beginning with the dog and cat, and finally, in the sublingual of the dog. We shall have to consider these points at greater length among other things in the third part of our work, in referring to the salivary glands. The reverse of all this takes place in other glandular organs, as, for instance, in the kidney, where the cells alloAV the secreted matters to pass through their membrane, repeating again Avhat occurs among the epithelia. The. question as to how gland cells are regenerated calls for renewed investigation. There can be but little doubt, hoAvever, that a process of segmentation takes place among them, for in many organs the occurrence of cells with tAvo nuclei is of great frequency (fig. 336, c; and 337, b). §197. The vascularisation of glands in keeping with their extreme vegetative energy is very perfect. The form of the vascular netAvorks is liable, how- ever, to great variation, being determined by the shape of the glandular elements. Thus race- mose glands are found to possess around their spheroidal A'esicles cor- responding bag-shaped Canillarv netAVOrks (fi°* F'£- 342.—CapiUary network from a racemose gland (the 342), like those of fat p"a"* lobules. On the other hand, tubular or follicular glands are supplied Avith a system of capillaries arranged in more elongated meshes or loops along their walls (fig. 327 and 343), not dissimilar at times to the mode of arrangement of the minute vessels in striated muscle. Around the outlets alone Avhen crowded together do the meshes again assume a cir- cular form (fig. 343 above, and 344 c). The vascular network of the 354 MANUAL OF HISTOLOGY. Fig, 343.—Network of blood-vessels from peptic gland of the human stomach. liver (fig. 345), is extremely dense surrounding the cells (comp. fig. 328), partly with roundish and partly Avith more or less radiating loops. With the exception of the latter anomalous organ, we never find the capillary networks situated actually among the groups of cells them- selves, but external to the mem- brana propria or envelope of connec- tive-tissue. In those cases in which the vessels penetrate into the interior through the enveloping structures, as in Peyer's glands and lymphatic knots, the part is improperly termed a secreting organ, and belongs rather to the lymphatic formations. The energetic transformation of material which takes place in glands, appears as a rule to necessitate the presence in them of lymphatics, an acquaintance Avith the nature of Avhich has recently been gained with greater accuracy than was previously possible. The testicle and thyroid gland (fig. 344, d, and 346, d-f) may be mentioned as examples. With the consideration of the nervous supply of glands, Ave come to one of the most obscure points in histology. The nerves here met with consist partly of Remak's fibres, and partly of medullary elements. Their distribution is in the first place to the blood-vessels of the organ, then to the excretory ducts and secreting elements of the latter. As a rule, hut few and scattered nerves , can be recognised in glands, but that several of the latter, as, for instance, the lach- rymal and salivary, are richly supplied with them has already been mentioned in a previous section (§ 189). Unstriped muscle may also be an important element in the structure of glands. Thus, without taking into consideration the muscular structures around the effe- rent ducts, Ave may see in the first place narroAv bundles, ascending betAveen the individual glands, as, for instance, in the mucosa of the stomach, or the same may be observed in the connective- tissue enveloping the several sub-divisions of the organ, as in the prostate and Cowper's glands (Koelliker). The Avail of the organ again may be muscular, as best seen in the large sweat glands of the axilla. The excretory passages of glandular organs must now be specially de- scribed. We have already seen that these are not indispensable to the Fig. 344.—From the testicle of the calf. At (a) the seminal tubules are seen somewhat from the side; at (b) trans- versely; c, blood-vessels; d, lymphatic passages. TISSUES OF THE BODY 355 proper conception of a gland, and even in cases in which the latter pos- sesses an outlet, there may be as yet no trace of a special canal for the carrying off of the secretion of the part. All simple follicular glands belong to the latter order, in which the form of cell changes just before the outlet is reached, but the ter- mination of the follicle itself is not clearly defined. In those cases only in Avhich several of the latter are united in one common, short, and Avidened terminal portion, can we speak of such a canal, as in those peptic glands of the stomach, in Avhich the portion common to the several tubules (Stomach cell of Todd and Boio- man) is marked by the difference of its columnar cells (fig. 347, a). The straight portion of the tubules of convoluted glands may be looked upon as an excretory duct, as it passes from the convolu- tion towards the outlet, although neither the structure of the wall nor the cellular lining is altered in the least; the diameter, however, decreases at first. On the other hand, among complex tubular glands, Fig. 345.—Network of vessels in tho rabbit's liver. Fig. 346.—From the thyroid of the infant, a, crypt of gland filled with cells alone; 6, incipient colloid meta- morphosis of the contents; c, the latter far advanced; d and/, large lymphatics; e, small lymphatics. Fig. 347.—A compound peptic gland from the dog. a, wide orifice of exit (stomach cell) clothed with columnar epithelium; b, point of division; r, single follicles lined with peptic cells; d, contents passing out. 2. The orifice (a) in transverse section. 3. Section through the several glands. such as the kidney, we find an elaborate system of excretory ducts lined 356 MANUAL OF HISTOLOGY. with clear, low, cylindrical cells, traversing the whole organ (fig. 348, a-d). We shall refer to this again. The ducts, or systems of ducts of racemose glands, however, are recog- nised by all. The most simple forms in Avhich these may be seen are to be found in the small glands of mucous membranes (fig. 349). Here we see the vesicles making up a lobule, continued into a shorter or longer passage of small diameter, whose wall is formed by a prolongation of the mem- brana propria. Among very small glands of this nature the junction of tAvo tubes, such as that just described, may constitute the whole duct of the organ (fig. 326). But in others the matter is not so simple, and in the larger mucous glands the common canal of exit from a group of lobules formed by the confluence of their ducts is but a branch of the true common passage. In the latter, or even in a branch of the first order of any considerable gland, we no longer find the simple homogeneous structure of the membrana propria; the walls are here composed of longi- tudinally arranged connective-tissue fibres, in addition to which an external stratum of looser texture may be remarked. They are lined, like- wise, within Avith a layer of epithelium cells. The length and breadth of these passages is sub- ject to much variation. What has just been described may serve as a key to the mode of formation of the larger and even largest glands. The subdivision and rami- fication of the passages in the latter has only advanced further, and the groups of lobules may be said to correspond to a certain extent to the individual mucous glands. The further diversity of form of organs of this kind depends, also, in a great measure on the peculiar course of these passages. Thus, in the pancreas Ave see the principal duct passing almost directly through the axis of the gland toAvards its apex. Many other organs, also, as, for instance, the lachrymal and mammary glands, are pos- Fig. 348.—From the kidney of the Guinea-pig, in vertical section, a-d, excretory; and e-h, secreting portion of the canal. Fig. 349. -Small mucous glands, some of whose ducts unite in a common outlet. sessed of several outlets : the union of the final twigs to form one common canal may be said in this case not to have taken place. In regard to the texture, in these instances Ave have presented to us in TISSUES OF THE BODY. 357 the finer ramifications the state of things already seen in the smaller mucous glands. The more considerable and terminal passages, however, acquire a tougher internal tunic, rich in elastic elements, which is enveloped in the external coat. Between these two layers there is inter- posed, further, in one class of glands a muscular sheath, consisting, when only slightly developed, of longitudinally arranged unstriped fibre-cells, as in the mamma and Cowper's glands. When more highly developed it is made up of an external longitudinal and internal transverse layer, to which may be added another still more internal of longitudinal fibres (vas deferens). The tunic situated internal to these, formed of connective- tissue, is gradually converted into a mucous membrane clothed with cylinder cells, and in it again minute mucous glands may appear (biliary and pancreatic ducts). §198. Turning now to the individual glands, the following points may be borne in mind : — 1. Among the tubular glands of the human body may be reckoned Bowman's of the regio olfactoria, Lieberkuhr's of the small intestine, the so-called foUicles of the large intestine, the peptic and mucous glands of the stomach, and the glands of the uterus. These all consist of follicles of varying length, formed of a simple membrana propria. Their length, which depends on the thickness of the mucous membrane, ranges from 0*2256 to 2*2558 mm. and upwards. In breadth they differ consider- ably; in Bowman's glands the diameter being 0*0323-0*0564 mm., in Lieberkuhn's 0*0564 mm., the large intestine 0*0564-0*1128 mm., and those secreting the gastric juice 0*0323-0*0457 mm. The number of these glands is often very considerable, so that they may cover the Avhole surface of the mucous membrane Avhen croAvded together, —as, for instance, the follicles of Lieberkuhn of the cat (fig. 350.) The tubes usually remain undivided, but in many glands, as those of the stomach and uterus, each may be split into two or three branches. The cells contained within them are partly flattened and round, partly cylindrical. Among the convoluted glands we have the smaller and larger sudoriferous organs, the cerumi- nous glands of the ear, and the tubules occurring in the conjunc- tiva at the edge of the cornea in many mammals. It is seldom that, as in the latter situation, they possess a simple membrana propria. In most the Avail is Fig. 350.—Lieberkuhn's glands from the cat (a), sur- . ,n • -i \ •„„ mounted by intestinal villi (b). stronger, this membrane being again enclosed within a layer of connective-tissue, betAveen which struc- tures muscular elements may be interposed as a middle tunic, e.g., the large sweat glands of the axilla, In this manner the Avails may attain a thickness of 0*0045-0*0094, or even 00135 mm. The breadth of the very long tubules of a convolution varies from 00451 to 0*0992, or even 01505 mm., and that of the Avhole of the latter from 0*2 to 6*7 mm. 358 MANUAL OF HISTOLOGY. Fig. 351.—Brunner's glands from the human duodenum, a, villi; b, bodies of the glands situated in the submucous tissue, which empty themselves through their ducts between the bases of the villi. The efierent duct is at first narroAv, later on expanded someAvhat, and loses its walls on penetrating the strata of the epithelium. The cells lining these glands are usually roundish and flat- tened, and possess a more or less fatty contents. The complex tubular glands present either a homogeneous membrane, as in the kidney, or this is replaced by connective- tissue, as in the testicle. The seminal tubules of the latter have a diameter of about 0*1128 mm., and the uriniferous tubes of the former range from 0*2 and 1*2 to 00377 mm. and upwards. These cells are polyhedral, calling to mind the appearance of flattened epithelium. The physiological pur- poses served by the several kinds of tubidar glands are exceedingly various. 2. The racemose glands constitute a very large group of organs, varying greatly both as to size, the character of the secretion yielded by each, and their physiological significance. To these belong the many small glands of the mucous membranes of the body. They occur with very dif- ferent degrees of frequency; often as, for instance, in the mouth and in the duodenum, they are very densely croAvded together (fig. 351). In different situations they are known under special names, as in the last case, Avhere they have obtained that of Brunner's glands. The sebaceous glands of the skin, likewise, Avith those modified forms of them knoAvn as the Meibomian of the eye- lids, belong to this same cate- gory. At the commencement of their development the first of these present themselves as simple flask-shaped follicles, which are subsequently converted by saccu- lation of their walls into smaller or larger racemose organs. Among the larger glands of this group may be reckoned the lachrymal, the various salivary glands, the pancreas, the mammary, Cowper's and Bartholin's glands in the organs of generation, as well as that aggregation Fig. a52.—From the thyroid of the Infant a-c, glandular spaces. TISSUES OF THE BODY. 359 of these structures knoAvn as the prostrate. The lungs might also be added here on account of their structure and development. The gland vesicles, almost always formed of a delicate membrana propria, vary in size from 0*1128 to 0*0451 mm., Avith extremes in both directions. The contents consists either of rounded, or more or less cubical cells. Some of them are filled with a fatty secretion. We have already considered their efferent ducts in the foregoing section. 3. Turning, finally, to those glands consisting of entirely closed roundish cavities, the thyroid (fig. 352) may be taken as the type. Here we find a number of short glandular spaces of roundish form in a ground- Avork of connective-tissue, having a diameter of 0*1128-0*0564 mm. and less, and consisting of a fibrous wall (Avithout any distinct membrana pro- pria) with a coating of small round cells. In the Graafian vesicle of the ovary, which is opened by rupture, and destroyed after expulsion of the ovum and remaining contents, Ave have another more complicated cap- sule, also imbedded in abundant, dense fibrous tissue. The interior is lined by minute, round, nucleated cells, in the midst of Avhich lies the primitive ovum. §199. As to the composition of glandular-tissue, to Avhich we will noAv deArote a feAV lines, it is one of the most neglected subjects in histology. Even of the nature of the membrana propria we knoAv but little : its substance, however, is no albuminous one. It consists rather of some material difficult of solution, and offering a tolerably prolonged resistance to the action of weak acids and alkalies, reminding us of the bearing of the transparent membranes of the eye. Its power of resisting concentrated alkalies is sometimes also considerable, in which cases this gland-enve- lope may consist of elastin, an important point when we take into account its indifferent nature and stability, and the great secretory energy of the organ. In other cases this membrane is not so durable, and we have not the slightest clue as to its composition. It need hardly be remarked that at those points where, instead of a transparent homogeneous mem- brane, a layer of connective-tissue presents itself, bounding the sub- divisions of the organ, we have to deal with a glutin-yielding substance. The gland cells, the most important parts of the organ in question,— those, m fact, which constitute them glands,—have but little remarkable about them excepting the contents of their bodies. Their membranes consist, for the most part, of a matter Avhich gives way even to the weaker acids, but sometimes of a material possessing much greater power of resist- ance, thus reminding us of many of the so closely allied epithelia. The nuclei present the same peculiarities here as elsewhere. The matters, however, contained in these gland cells vary with the species of secretion to be produced. Thus, for instance, we meet with materials in the cells of the liver Avhich are subsequently found free in the bile,—such as fats, pigments, and glycogen, which leads to the forma- tion of sugar, and is carried off Avith tlie blood of the hepatic vein. In the cells of the mammary gland, further, we have the butter fats of the milk; in those of the sebaceous glands, the fatty matters observed on the skin * in the gastric cells, the pepsin found in the juices of the stomach, and so on. Mucin also is contained, together with other substances, in those cells held to be the generators of mucus. Kow, although the components of the secretions present themselves 24 360 MANUAL OF HISTOLOGY. first as constituents of the gland cells, Ave find, nevertheless, that they differ among themselves in two particulars. In the first place we remark, that in a certain number of the organs in question these substances are only abstracted from the blood to sojourn simply in the body of the cell for a longer or shorter space of time. This is the case, for instance, with the constituents of the sweat glands and kidneys, in Avhich Ave are unable to demonstrate any notable chemical metamorphosis through the agency of the cell. The latter may, however, be evident, though in a minor degree, in other glands, for instance in the female breast, in which an albuminous substance is transformed into casein, and, Ave suppose, grape sugar into sugar of milk. Such instances are connecting links betAveen the first case and another, in Avhich the cell produces, by the disintegration and rearrangement of the matters it receives, completely neAV and peculiar substances, as may be seen in the liver, in the production of the bile acids. Another difference concerns the cell itself, as Ave know already. This may either be cast off after the generation of its specific contents, setting free the latter (sebaceous, milk, and peptic cells), or the contents may escape from its uninjured body, Avhile it itself remains as a permanent structure (renal and hepatic cells). Finally, the "egotistical" mutation of matter of glandular tissue, i.e., that which takes place in the interest of its own proper nutrition, must give rise to the generation of the more general decomposition products of the system. Thus, according to Staedeler and Frerichs, leucin has been found in exceedingly small quantity as a very general transforma- tion product in glands, seldom in larger amount, as in the pancreas. Other bases, such as tyrosin, tauiin, cystin, hypoxanthin, xanthin, and guanin, appear more rarely. Inosit and lactic acid may also be met Avith, and uric acid, though with less frequency. These matters are partly dis- charged with the secretions of the glands, and partly taken up again into the circulation. Later on, in considering the salivary glands, Ave shall see the control Avhich the nervous system possesses over the chemical action of these organs § 200. Turning now to the development of glands, it will be remembered that the epithelial nature of these structures has already been touched on. The mode of origin is the best proof of this. It is well known that a Avhole series of glandular organs is derived from the external cellular layer of the foetal body from the so-called corneous leaf. They commence in the form of nodulated prolongations downwards of the epithelial cells, in which at first no trace exists of either central cavity or gland-mem- brane. This latter is subsequently formed on the exterior of the aggrega- tion of cells as a deposit. The size of this mass is increased by division of the cells of Avhich it is composed, Avhile the connective-tissue surrounding it becomes eventually the envelope of the gland. Among the structures so formed may be mentioned the sweat, mammary, and lachrymal glands. The sweat glands (fig. 353, a) are developed, according to Koelliker, ' after the fifth month of intra-uterine life. Commencing as small flask- shaped growths formed of the rete Malpighii cells, they advance deeper doAvnwards through the skin in the following months, becoming eventu- ally curved, in a gradual manner, at their loAver end. Then a trace of the central passage and external outlet becomes apparent. The sebaceous TISSUES OF THE BODY. 3G1 glands also, the first rudiments of which may be observed someAvhat earlier than in the preceding case, are likewise solid lateral groAvths of the undermost cells constituting the rudiments of the embryonic hair follicle, and possess the same flask-like form. The cells in their interior begin very early to undergo that so characteristic fatty infiltration with Avhich Ave are already acquainted, at the same time increasing in volume. Then by continuous groAvth they gradually form those vesicular lobules mot Avith in the fully matured structures. The mammary glands, again, are developed in a manner precisely similar, from the fourth and fifth month on. Around the several aggregations of cells (fig. 354) an external connective-tissue envelope may be seen, a doubling in of the skin. But it is only at the period of puberty and pregnancy that the organ attains a state of perfect development. Fig. 353.—Sweat glands of a foetus Fig. 354.—The mammary gland from a tolcr- at five months, a, superficial, b, ably mature embryo, alter Langer. a, the deeper layer of the epidermis; the middle nodulated portion with shorter excre- rudiments of the gland are formed scences; 6, and longer. by the exuberant growth down- wards of the latter. As to the germ-producing glands, the OAraries and testicles, as far as concerns their cedular elements, Ave are still, unfortunately, in the dark in spite of numerous investigations. Besides those just mentioned, there are a great number of organs of the same nature, whose development takes place on a precisely similar plan, from the so-called intestinal glandular embryonic plate. Among these may be reckoned the glands of the digestive apparatus and the larger organs connected with the latter, e.g., the liver, pancreas, and lungs. Here, instead of the cells of the corneous layer, Ave have before us the elements of the glandular leaf arranged over the surface of the tube as intestinal epithelium. The mode of formation of these, hoAvever, is but imperfectly knoAvn, as, for instance, that of the peptic glands and follicles of the large intestine. The follicles of Lieberkuhn appear, on the other hand, to consist, from the very commencement, of holloAv duplicatures. The first rudiments of Brunner's glands, hoAvever, as Avell as those of the remaining racemose mucous glands, are formed of solid masses of cells. The salivary glands seem to be formed on an analogous plan of develop- ment, except that a far more extensive proliferation of the cells takes place, producing roundish aggregations of the form of the vesicles of the organ. The pancreas commences also in a IioIIoav duplicature, Avhose clothing of cells gives rise by a similar process to the various lobules and 362 MANUAL OF HISTOLOGY. vesicles of the organ. The formation of the lungs is carried out on a simdar plan. 17. The Vessels. §201. Of a special vascular tissue, or tissue peculiar to vessels, we can only speak in a very limited sense. The most internal layer alone consists everywhere of a series of flattened cells of a peculiar kind, cemented together at their edges, and resembling very closely epithelium. The walls of the finest and most simple tubes are composed solely of these cells. All the remaining coats, on the other hand, which strengthen the walls by being laid down around them (and they are seen very early) are formed of muscular and elastic tissue, of structures, therefore, to which Ave have already given our consideration. But in that the fine tubes with their simple texture are continuous through the most gradual transitions with those of wider gauge and more complex structure, a general glance at the blood-vessels and lymphatics will be found useful. It is well known that the canals of the vascular system are classified into those which convey the stream of blood from the heart, called arteries, those which collect and bring back the same known as veins, and those which are interposed between these two, forming a system of fine hair- like tubes, to which the name of capillaries has been applied. The latter, compared with the merely con- ducting veins and arteries, constitute the most important part, physiologi- cally, of the whole, in that through their delicate Avails the interchange of matter betAveen the blood and organic fluids, as well as secretion, takes place. The capillary vessels present for our consideration, as a rule, a wad quite distinct from the neighbour- ing structures. For those so con- stituted we Avould retain the name of capillaries. In other and rarer instances, this tube containing the blood is fused with the adjacent tissues, the fluid, as it were, flowing through grooved passages, in which case we have the capillary canal. Finally, recent observations seem to teach that in the pulp of the spleen the finest streams of blood actually flow through membraneless inter- stices. These latter are known as capillary lacunar. Capdlaries of the smallest calibre, which do not, however, occur in all Fig. 355.—Fine blood-vessels from the pia mater ■if the human brain. A, a small branch, which divides above into two delicate capil- laries, a, 6, and which consists below (d), of two tunics; B, a similar tube, with branches; C, a vessel of greater calibre, with a double mem- brane, the internal (a) showing longitudinally arranged, and the external (b), as well as intermediate, transverse nuclei. TISSUES OF THE BODY. 363 parts of the body, are tubes just sufficiently large to permit the passage through them of a single blood corpuscle, which can even be compressed in its course. The diameter of the lumen may be stated consequently at 0*0045-0*0068 mm., whilst other and more considerable tubes attain a breadth of 0*0113 mm. and upwards. These canals (355, A, B) were supposed, until very recently, to have an extremely simple texture. As a rule, their Avails are perfectly trans- parent and structureless, and endowed with remarkable elasticity and extensibility. Chemically, they resemble the sarcolemma of muscle fibres and primitive sheath of nerves, displaying a considerable power of resisting the action of many strong reagents. In the walls of these tubes rounded or oval nuclei are to be seen, 0*0056--0*0074 mm. in diameter, in which nucleoli may be remarked. These are arranged irregularly one behind the other at considerable intervals (A, a, b, B, a), but at times at more regular distances (A, a, B, b). In larger branches, measuring perhaps 0*0113 mm. and upAvards, the latter arrangement is the rule; otherwise the structure remains the same, except that such tubes may attain considerable thickness, amounting to 0*0018 mm. The long axis of the nuclei corresponds to that of the vessel; they are conse- quently said to be longitudinally oval in figure. §202. This view just mentioned of the nature of the walls of capillaries was held for many years with unquestioning tenacity, no expedient having as yet been hit upon by which the structure of the trans- parent nucleated membrane of which they consist could be farther resolved. However, all at once the analysis of structure Avas accomplished through the discoveries of Auerbach, Eberth, and Aeby following in the footsteps of Hoyer. From them we learned the usefulness of very dilute solutions of nitrate of sdver in rendering visible, in the most exquisite manner, the delicate contour of cells (whether those of epithelium or smooth muscle) in the form of dark lines. The transparent nucleated membrane in question is formed of flat cells, often peculiarly bordered, and having a single nucleus (figs. 356 and 357); they are united closely with one another at their edges, and curved toAvards the lumen of the vessel. The tube thus formed is endoAved, moreover, with vital contractility (Strieker). These cells, further, extend continuously into the more considerable and even the largest trunks, though to a certain extent modified. This may easily be re- cognised. Here they were known even to the earlier histologists, their contour being plainly visible Avithout any further treatment. They Avere described as the epithelia of the arteries, veins, and cardiac cavities (§ 87), and we may add, with perfect correctness, for these lining cells of the vascular system are members of the epithelium group ofthe middle germinal layer (pp. 158, 159), the endothelia of His. Another name has been proposed for them also by Auerbach, namely, perithelium. It may be found more convenient, how- Fig. 356. — Capillaries from the mesentery of a Guinea-pig after treatment with solu- tion of nitrate of sil- ver, a, cells; b, nu- clei of the same. 364 MANUAL OF HISTOLOGY. ever, if, for the future, we make use of the term primary vascular mem- brane in referring to this cellular tube. In regard to the cells themselves, they are presented to us according to the breadth of the tube, either under a more or less fusiform or polygonal form. The first variety (fig. 356), bounded by delicate serrated or undulating lines, have a length of 0*0756-0*0977 mm., and breadth of 0*0099-0*050 mm. Such ele- ments are to be found forming the walls of the finest capillaries,t arranged either parallel to the axis of the vessel, or more rarely obliquely, as regards the latter. In transverse sections of the vessels two or three, or less frequently four of them, may be remarked. In many of the finest vessels portions of the tube are formed of one single cell alone, its two edges meeting around the lumen. Such cases may be found among the capillaries of the brain, the retina, the muscles, and the skin. Capillaries of larger calibre are made up of cells of the second variety. We encounter here either regular polygons, as, for instance, in the chorio-capillaris of the cat and iris of the bird's eye, or more irregular Fig. 357.—Capillary network from the lung of the frog treated with solution of nitrate of silver. 6, vascular cells; a, nuclei of the same. Fig. 358.—Capillary ves- sel from the mesen- tery of the frog treated with nitrate of silver. Between the vascular cells at a, a and b, the "stomata" are to be seen. Fig. 359.—Capillaries and finer trunks from a mammal, a, capillary from the brain; 6, from a lymphatic gland; c, a somewhat stronger branch, with a lymphatic sheath, from the small intestine; and d, transverse section of a small artery of a lvmphatic gland. plates (fig. 357), in many instances giving off long processes. In the transverse section of the vessel we may have tAvo or four of these. In size they are naturally subject to great variation, and may attain a diameter at certain points of 0*0749-0*01737 mm. The interdigitation of their TISSUES OF THE BODY. 365 processes presents a most peculiar appearance under the microscope. Be- tween these cells, however, may be observed a greater or smaller number of roundish marks of varying size, sometimes in the form of a dark spot (fig. 358, a, a), sometimes in that of a ring (b). These have been hitherto held by manyr to be preformed openings or "stomata," and to account for the exit of white and coloured blood cor- puscles (p. 128). The recent investigations of Arnold also have confirmed the correctness of this view. Noav, whilst we believe that in many parts of the body the whole of the capillary vessel is represented in this cellular tube just mentioned, there are some localities in which the latter is enveloped in a delicate homo- geneous membrane, probably the first indication of the tunica intima. There are again places in which the surrounding connective-tissue forms an external envelope for all capillaries, even the most minute,—in fact, an adventitia capillaris, which may be regarded as equivalent to the tunica cellulosa of larger trunks. Thus we find the capillaries of the brain (fig. 359, a) enclosed in a homogeneous nucleated membrane, and those of lymphoid organs (b) closely invested in reticular connective substances. Again, other more considerable, but still capillary vessels, may be enveloped loosely in a layer of connective-tissue (c), and the space thus left between the latter and the vessel may serve the purpose of a lymphatic passage. We shall refer again to these lymph sheaths, and only stop to remark here, that every adventitial tissue of a blood-vessel containing lymphoid cells, must not be regarded as one of the latter. Another circumstance also may frequently give rise to the deceptive appear- ance of such a sheathing, namely, that a blood-vessel is often bounded on each side by lymphatic canals • this is most commonly seen in uninjected preparations. Noav, although in those cases just described the capillary wall is easy of recognition in it own individuality, there are others in which the cells of the tube become so intimately united with the adjacent tissues, that they are either totally inseparable from the latter, or only so with the help of the stronger reagents at our disposal, although treatment Avith nitrate of silver naturally renders them visible. This is the texture of the capillary canal as found, for instance, in the membrana pupillaris of the foetal eye, the skin, and other strong fibrous structures. § 203. Passing on uoav from these finer forms to the larger trunks, Ave meet again with those layers already knoAvn to us, namely, the epithelial, and the intima enveloping it, and finally the external fibrous coat. The latter appears in the form of longitudinally striated connective-tissue, Avith vertically arranged nuclei or connective-tissue corpuscles. Very soon, howeA*er, even in extremely fine trunks, especially as we pass toAvards the artery, betAveen the two internal membranes and the external coat, a thin layer of transversely arranged contractile fibre cells may be observed. Avhose nuclei we may easily detect. The latter are spoken of as transversely oval. There can be uoav no doubt but that in this we have before us the first rudiments of the middle or muscular coat of the larger trunks. Once more to recapitulate: Ave see first (a) the layer of flattened cells, then (b) the longitudinally streaked internal coat, then (c) the transverse 366 MANUAL OF HISTOLOGY. muscular elements as middle coat, and finally (d) the external envelope of connective-tissue. Vessels of this kind can by no means be called any longer capillaries; a- 4 Fig. 360.—Two considerable vessels from the pia mater of the human brain. 1. A small arterial twig. 2. A venous twig; a, b, internal; e. middle; and d, external layer. they bear from henceforth far more the character of fine arterial and -* venous branches. According to their nature in this respect, they offer certain differences for our consideration, and besides,a series of others of a more local or indi- vidual kind. Taking vessels of about 0*0282- 0*04512 mm. in diameter (fig. 360), only two membranes are to be dis- tinguished in a venous branch (2) of this kind. In the first place an inner (a, b), in the form of a toler- ably resistant elastic tunic, re- markable for its tendency to form smaller or larger longitudinal folds, and studded with numerous nuclei. The latter on treatment Avith silver are seen to be the nuclear formations of the vascular cells, which are smaller here than in the capillaries, presenting also a broader and more rhomboidal figure. It is still a matter of uncertainty Avhether these are again clothed in a thin longitudinally marked Fig. 361.—An arterial branch. At (b) the homo- geneous internal layer destitute of nuclei; (c) mid- dle tunic formed of contractile fibre cells; d, the external connective-tissue tunic. TISSUES OF THE BODY. 367 coat or not. The second layer (d) presents itself in the form of a streaky- fibrous tissue envelope with elongated nuclei and connective-tissue cor- puscles. If we compare with this an arterial branch (1), Ave find again the two coats (b and d) just described; but between the inner membrane and outer tunic of connective-tissue there now appears a layer of trans- versely arranged contractile fibre cells lying side by side (c), whose elongated nuclei present themselves in transverse sections of the vessel as encircling the latter. This tunic is of varying strength. In other arterial twigs it may appear with greater distinctness, either as a single or multiple layer. Fig. 361 represents this in a side vieAv, and fig. 359, d, the transverse section of a small artery with laminated muscular coat, and an adventitia consisting of reticular connective-tissue. The epithelium cells are narrower here than in the veins, but much more elongated in the direction of the vessel, and fusiform. § 204. • Thus far is it possible to subject the blood-vessel as a Avhole to micro scopical analysis. Larger tubes must be examined in their various parts, either by rending the Avails, peeling off layers with a forceps, the vessel having been slit up, or by preparing sections of the previously dried or hardened wall. The further changes from the next in order to those occurring in the formation of the largest vessels, consist in this, that all the layers, Avith the exception of that formed of endothelial cells, which remains single, commence to become more and more laminated, especially the internal and middle, thus collectively bringing about an increase in the whole thickness of the vessels. The internal strata preserve in their systems of membranes arranged in laminae one over the other their elastic character, presenting every variety of elastic tissue in longitudinal arrangement. The middle coat is transformed into a system of laminae of smooth muscle fibres, connective and elastic tissue, with a transverse direction. The external tunic, finally, becomes thicker and thicker in its connective sub- stance Avith an ever increasing development of elastic networks. Fig. 362 represents at (1) the umbilical artery of a foetus of eight months old in transverse section, and at (2) a large artery from the adult similarly cut, and gives us for the present an idea of the arrangement of parts in question. The distinction between the different coats becomes, however, less and less apparent at the same time. We must, however, bear in mind that the coats of veins are thinner than those of arteries of corre- sponding calibre, a circumstance which depends upon the minor develop- ment in them of the middle tunic. The endothelial cells of venous vessels preserve everyAvhere the same short broad figure already men- tioned in the foregoing §. Small veins, merely higher grades of development of such a vessel as that represented in fig. 360 (2), commence much later to acquire a muscular layer than arteries of the same magnitude. A venous vessel, for instance, of 0*23 mm. in diameter offers for our consideration an internal membrane in which may be observed elastic longitudinal interlacements, a feAV laminae of muscle-fibres in the middle coat, intermixed with elastic net- works and layers of connective-tissue, and, finally, an external thicker coat, formed of fibrillated connective-tissue and elastic fibres. In medium-sized veins the internal coat consists of either one or several 368 MANUAL OF HISTOLOGY. laminae, longitudinally streaked and studded with nuclei and fusiform cells, and a stratum of elastic membranes and fibrous networks arranged longitudinally, between which the elements of smooth muscle may even be insinuated. The middle tunic is formed of obliquely-crossed fibrous tissue, with elastic netAvorks, whose fibres take the same direc- tion, and also of unstriped muscle cells. Between these there ap- pear, however, elastic membranes, Avhose fibres maintain a longitu- dinal course. The middle layer of vessels of this kind is, as a rule, much weaker than that of arteries, but is rich in muscular elements. The strong external coat is formed of connective-tissue with elastic interlacements. Un- striped muscle may, however, also occur. The largest veins of all, finally, present a similar arrangement of their internal laminae, except that the latter have no unstriped muscle fibres, while the middle layer remains comparatively un- developed, or may in rare cases be entirely absent. The muscle elements of the latter when pre- sent are scanty, and accompanied by abundant connective-tissue, whose fibres are obliquely ar- ranged. Elastic fibrous netAvorks of longitudinal direction are also present still. A strange pecu- liarity has been remarked here in the usually strongly developed external layer of many veins, namely, the occurrence of a large amount of longitudinally arranged muscle, which generally occupies the internal portion of the former in varying strength : it is mixed Avith fibres of connective-tissue taking an oblique course. There are certain veins, indeed, which shoAv an excessive development of these muscular elements, as, for instance, those of the preg- nant uterus; in others they are entirely absent, as in the sinuses of the dura mater. The valves of veins, which are covered with endothelium, consist mainly of connective-tissue interspersed with elastic fibres. In small arteries the internal and external layers remain comparatively Fig. 362.—Transverse sections of arteries. 1. The umbilical of a human foetus eight months old. a epithelium; b, layers of the internal coat; c, the muscular layers of the middle coat without any intermixture of elastic elements; d, external cover- ing, made up of colloid tissue. 2. A large artery from the adult; a and b, as in fig. 1; c, the line of demarcation between the inner and middle coats; d, elastic, and e, muscular laminae of the middle coat; g, the external tunic traversed by elastic networks; at/, below, the latter are highly deve- loped. TISSUES OF THE BODY, 369 unchanged. The former, hoAvever, may frequently acquire the characters of a reticular elastic tunic, owing to incipient absorption at certain points; this is the so-called fenestrated membrane (§ 127). Condensation may also lead to the formation of an elastic network stretched in the direction of the axis of the vessel. The middle layer consists of several strata of transverse unstriped muscle-fibres, laid one over the other. In the outer, finally, the connective-tissue becomes fibrillated, and the corpuscles of the latter unite to form fine elastic fibrous networks. We must be permitted here to refer, in a feAV words, to the umbilical arteries (fig. 362, 1). These are remarkable for the extraordinary development of their muscular middle coat (c). As tunica adventitia we find (d) a reticular connectiA'e substance, already seen in the gelatin of Wharton (p. 191). The arteries of the ovaries likeAvise have very strong muscular tunics. The latter may attain an enormous pitch of develop- ment in the branches supplying the so-called corpus luteum. Trunks of more considerable magnitude, of about 2 mm. in diameter, for instance, show in their internal coat an increase of elastic tissue, in addition to Avhich longitudinally striated layers may occur. There are likewise inter- posed between the greatly thickened laminae of muscle fibres imperfectly developed membranes of elastic nature, with webs of elastic fibres holding an oblique course ; the latter attain also, in the outer tunic, a high pitch of development. In vessels of larger diameter still these elastic networks are developed more and more, especially internally, toAA*ards the tunica media. Turning now, finally, to the largest arterial trunks of the body (fig. 362, 2), we find, in the first place, that the internal layer (b) has increased in thickness by multiplication of its elastic laminae. These latter present themselves, in keeping with the variability of elastic tissue, either in the form of membranes or of membranous networks stretched in the long axis of the vessel, or again as fenestrated coats. More internally, close to the epithelial layer, may be seen laminae, either homogeneous or longitu- dinally striated, in Avhich, as for instance in the ascending aorta, networks of stellate cells exist, lying one over the other, as was discovered by Langhans and confirmed by Ebner. In the middle coat (d, e) the mem branous character of the obliquely running elastic Avebs becomes more and more marked. The latter may be very thick, or, again, fine and delicate, and the Avhole present a fenestrated appearance, owing to absorption of the interstitial connecting substance. As a rule, these membranous elastic layers, whose number may amount to from thirty to fifty and upwards, are interleaved Avith tolerable regularity with the laminae of the muscular substance (e). The latter presents itself in varying degrees of perfectness, and is frequently but slightly developed, which may depend upon the high degree of development of the elastic intermediate layers : its direction, like- Avise, is by no means always the same. In the outer portions ofthe middle tunic fibrillated connective-tissue is also to be found (Schultze, von Ebner). In the most external coat (g) the elastic networks are frequently more and more strongly marked at its inner portion (/), so that among the larger mammals, as, for instance, in the whale, they furnish one of the strongest examples of elastic tissue that can be met with. As an exception, smooth muscle may also make its appearance in the internal coat of human arteries. Corresponding muscle elements to those Ave have described as occurring in the external layers of the veins appear to be entirely absent in the arteries of the human body. Commencing even in the smaller tAvigs, the blood-vessels are supplied 370 MANUAL OF HISTOLOGY. Avith arteries for the nutrition of their Avails. These are known as the oasa vasorum, and are distributed, for the most part, to the middle and external coats, and especially to the latter, in which they are tolerably numerous. They are here arranged like those of formless connective- tissue, except that they form narroAver meshes. Later on they appear in the middle layer, where they have been seen in arteries to form vascular networks of fine tubes, with elongated oblique meshes (Gerlach). The nerves of arteries derived from the sympa- thetic and cerebro-spinal system are distributed in the larger trunks to the middle and external tunics. As a rule, the arteries seem to be richer in nerves, on account of their thicker middle layer, than the veins, but the greatest variety exists in this respect. All that is necessary has already been remarked in respect to the termination of the nerve3 of vessels in § 183. §205. We mus now turn to the more careful considera- tion of the capillaries as to the most important subdivision of the vascular system. We have already seen that no sharp boundary can be draAvn between these vessels and the arteries and veins, in that the most imperceptible transition exists from one to the other. But one thing is char- acteristic in the capillaries, namely, that their tubes no longer decrease in calibre from the giving off of branches, and that they form among themselves, in the various organs supplied by them, netAvorks of tolerably regular size and shape (fig. 363, c, d). The diameter of the vessels so connected is, Iioav- ever, by no means the same in the various organs, and the finest are not presented to us in every locality. The brain and retina possess the most delicate. Their transverse diameter in these organs may be stated at 0*0068-0*0065 mm., or, in some cases, even so low as 0*0056 mm. In muscle they appear to be somewhat larger, measuring 0*0074 mm. Those of the connec- tive-tissue of the skin and mucous membranes, again, are still larger. In most glands, as, for instance, the liver, kidneys, and lungs, the diameter of the capdlaries lies between 0*0091 and 0*0135 mm. The largest of all vessels of this kind are to be found in bony tissue, where they measure as high as 0*0226 mm. It must be borne in mind, hoAA-ever, that, owing Drw, •- ... . .. to the elasticity of the capillary tube, and its variation in diameter according to the amount of blood contained m it, these measurements can only be regarded as approximate. Fig. 363.—Vessels of striped muscle, a, artery; b, vein; c and d, extended capil- lary network. Fig. 364.—A pulmonary alveolus from the calf a, large blood-vessel; b, capillarv network- c, epithelium cells. ' TISSUES OF THE BODY. 371 Fig. 365.—Vessels from the human retina, a, arterial b, capillary network; c, venous twig. In other vertebrates, likewise, the size of the capillaries must be greater to correspond with the larger dia- meter of the blood corpuscles. Touching now the distances between the tubes, and the greater or less vascularity of a part depending thereon, the most remarkable variety pre- vails. The lungs, the glands, the mucous membranes, and the skin are the most vascular of all struc- tures ; whilst other parts, such as the serous and fibrous mem- branes and the nervous trunks, are very poor in vessels. The vascular netAvorks of the lungs (fig. 364) and of the retina (fig. 365) afford examples, although the latter membrane cannot be reckoned among those poorest in blood in the body. Finally, Ave know of tissues Avhich contain no blood-vessels, such as the cornea, the lens cartilage, the epithelial structures, and nails. It is easy to conceive that, OAving to the minuteness of the elements of form, only consider- able groups of the latter can be surrounded by the capillary net- works in organs with a small amount of vascularity. But even in those parts most abundantly supplied with blood the capillary tube always lies external to the elementary structure, and never penetrates into the interior; at the very most, is each individual form element surrounded with a single loop, as in the case of the fat cell (§ 122) and muscle fibre (§ 168). The forms under Avhich capillary networks pre- sent themselves are very nume- rous, and at the same time fre- quently so characteristic of the various parts to which they be- long, that the practised eye can often recognise an organ from a section of its substance Avhich has been injected. These forms are chiefly deter- mined by the texture of the part and the grouping of its structural elements, Fie 366 —Vessels from about fat cpUs. A,an arterial twig at a, and venous at b, with round capillary network of a fat globule. B, the capillaries of three free cells of the latter. 372 MANUAL OF HISTOLOGY. as well as the shape of the latter (fig. 366, A, B). Thus, around certain globular structures, such as fat cells and the terminal vesicles of racemose glands, Ave find bag-like nets of vessels, and also about the outlets of follicular mucous mem- branes a circular interlacement of the latter. The cells of an hepatic lobule, Avhich have a radiating arrange- ment, as depicted in fig. 328, p. 345, produce also a radiating course in the capillaries of the net- Avork of the part, Avhich is pri- marily bag-like (fig. 367). Again, in those parts whose structural ele- ments are elongated and regularly grouped, Ave find the meshes of the vascular web likewise much drawn out, as it were, and very narroAv, as, for instance, in muscle (fig. 363, c, d"}, in nerves, in follicular or tubular glands, such as those of the stomach (fig. 343, p. 354). Fig. 368.—Capillary loops from the sensitive papillae of human skin. Fig. 369.—The vascular loop network of an intestinal villus. a, arterial twig; b, capillary net with its circular arrange- ment around the outlet of the Lieberkuhn t follicle at d • c, venous branch. Fig. 367.—Capillary network from a rabbit's liver. TISSUES OF THE BODY. 373 It is easy to conceive also that each form of netAvork may make its appearance Avith ever so many different modifications. On account, for instance, of the narrowness of the space in such conical protuberances as the sensitive papillae of the skin and papillae of the mucous membranes, regular capillary loops, as they are called, may be formed (fig. 368). Again, if these cones attain much greater dimensions, as in the villi of the small intestines, an arrangement of capillaries is brought about which is known under the name of the loop network, a further complication of the former. In this case we see, passing between the two or more principal vessels of the sling, a finer set of tubes holding a trans- verse course (fig. 369, b). Finally, in this sketch may be in- cluded the glomerulus, as it is called, of the kidney, an arrangement of vessels peculiar to, and characteristic of, that organ (fig. 370). Here Ave find a minute arterial twig (b), micro- scopically small indeed, suddenly curled upon itself in a manner similar to the inferior portion of a sweat gland (c). Within the COn- Fig. 370.-Glomerulus from a pigs kidney , .. ., v '.. .. . (half diagrammatic), a, arterial branch; 6, VOlutlOn it may divide into branches the twig supplying the convolution; c, glo- tn a rwrnin pvfpnt i« in nun nnrl Hin merulus; d, efferent vessel; ef, capillary 10 a Certain extent, as in man ana tlie network emptying itself into a venous twig mammalia, or remain single, after at g- 394.—Cuticle from the shaft of the on the outline of the hair, owing to their nSVvmass.ui^thMTot8. upper free edge projecting from the shaft in the form of small ridges. To show them properly, we have recourse to the action on the tissue of solutions of soda, or, better still, of sulphuric acid. There stid remains for consideration the axial or medullary mass of the hair (2). This is, however, no essential constituent of the structure in question, in that it is not to be found as a rule in doAvny hairs, and is frequently absent in part or entirely in those of the head. It presents itself in the form of a streak in the centre of the stem, occupying about a fourth of the thickness of the latter (fig. 392, m, n; 394). Whdst at the boundary betAveen the bulb and commencement of the shaft the external cells become elongated, and the transformation into the characteristic hair-plates commences, those situated internally assume a more or less angular form as they become arranged in several layers and increased in size until they may measure 0*0151-00226 mm. These soon lose their nuclei and dry up (fig. 392, k). On the other hand, small cavities are found in great number and most extensively in the contents of the cells, which become filled with corresponding bubbles of air, pre- senting, OAving to their tiny proportion, the appearance of fatty or pigmentary molecules (fig. 392), which they were long supposed to be. They communicate to the medullary substance of Avhite hair a silvery appearance with reflected light, Avhdst in coloured hair, whatever be its tint, the Avhite axial portion shines through. By suitable treatment we are able to expel the air from the medulla in the same manner as from a thin section of bone, Avhen, on subsequent drying, it rapidly fills again. Remarks.—On the upper edges of the cuticular cells becoming more everted the transverse lines appear with greater distinctness. Hairs which have been torn out 394 MANUAL OF HISTOLOGY. frequently display an extensive folding back of the cells toward* thie bulb, gmng ne to the appearance of encircling fibres. 2. The medullary portion of the ha,"the on lj part about which there exists at present any considerable M™™e/°%™n{* ^ presence in it of air was first pointed out by Griffith in the Lond. Med. Gazette, 1848, p. 844 On this point no doubt can be entertained. Steinhn held the medullary mass to be a process of the papilla of the hair, consisting of cells, and extending into the shaft. The lower part is, according to him, vascular, and made up of soft cells, while above, the vessels become obliterated, and the cells shrink, making room for the accommo- dation of air, so that the medulla might be said to be formed from the dried papilla. Reiehert supposes the dried remainder of the papilla to occupy the interior of the medulla in the form of a delicate axial thread, and likens it to the " pith of a feather. In some of the mammalia such an extension of the papilla into the shaft of the hair does take place, and even far up into the latter, but in man it is doubtful that this occurs. The representation given in the text is that most generally received, and probably the simplest expression of observation. It is likely also that many com- munications exist between the residual cells, which explain the rapid readmission of air, §216. The hairs, like cuticle and the nails, are numbered among the so-called. horny tissues, in that from them all, by treatment with alkalies, that mixture of metamorphosed albuminous matters can be obtained, to which the name of keratin (p. 21) has been given. The complex structure of fhe hair, however, renders this analysis of less value than that of the tAvo other more simple tissues. Microchemical reaction shows that, in the hair and its envelopes, the young recently-formed cells are still composed of ordinary albuminous materials, so that even the more feeble attacks made by acetic acid and dilute solution of the alkalies are capable of destroying their membranes, and, soon after, the nuclei in the case of the latter reagents. This is the case with the rete mucosum of the hair follicle, the external root-sheath, and also the root of the hair. On the other hand, we are met by a most striking insensibility to the action of chemicals in the cellular layers of the internal root-sheath and cuticle of the hair, with the exception of the most internal portion of both tissues bordering on the bulb. We find that even concentrated sulphuric acid and alkaline solutions have no action on the cells, even when the latter are treated for a considerable time with these fluids. The latter do not even produce any amount of swelling up in the elements, so that we have at all events peculiar kinds of combination before us in these tissues. The action of sulphuric acid on those dry and horny cellular plates Avhich form the cortical portion of the hair, causes them to separate readily from one another, Avhile alkalies produce a SAvelling up of the cortical mass, and solution of the Avhole when dilute and at an elevated temperature. The cells likeAvise of the medullary mass can be recalled from the shrunken condition in which we find them in the mature hair to their original tense round form by these reagents. The transparent internal layer of the follicle, finally, manifests, as has been already mentioned, all the insensibility of the elastic hyaline membranes. The solubility of hair in solutions of soda and potash, with previous swelling up, repeats, as we have already stated, what takes place with epidermis and nail tissue under similar treatment. The products of the combustion of hair also are similar to those of the latter. An analysis of Van Laer's will serve,as an example :— TISSUES OF THE BODY. 395 C . . . 50*65 per cent. H . . . 6*36 N . . . 17-14 0 . 20*85 S 5*00 The amount of sulphur, 4-5 per cent., seems considerable. But little is known at present of the nature of that diffused colouring matter which saturates the cortical tissue of the hair, or of the oranular ♦ pigment of the structure. Those fatty matters Avhich may be extracted in varying amount from hairs appear to contain the ordinary neutral combinations found in other parts of the system. They probably have their origin, for the most part, in the sebaceous glands. The ashes of hair amount to from 0*54 to 1*85 per cent. They consist of salts soluble in water, together with phosphate and sulphate of calcium, silicates and oxide of iron (0*058-0*390 per cent.) Manganese, although formerly stated by Vauquelin to exist in the hairs, has not been found by chemists of a later period. That the presence of iron has anything to say to the tint of the latter is very improbable. §217. Hairs are to be found on almost every part of the human body. They are missed, however, on the upper eyelid, the lips, the palm of the hand and sole of the foot, the last joints of the fingers and toes, the inner surface of the prepuce, and on the glans penis. Their size, further, is liable to considerable variation, as we may see from the range in their diameter from 0*15 mm. and upAvards down to even 0 0153 mm. A distinc- tion is always made betAveen the very pliant downy hairs (lanugo) and those which are stronger, sometimes pliant and sometimes stiff. No sharp distinction, however, can be drawn between them. The thickest are those of the beard and pubis. The length of the free portion also varies extremely, ranging from 1-2'" among the smaller doAvny hairs, to 4-5', as on the heads of women. Many hairs, notwithstanding their thickness, remain exceedingly short; this is the case in the eyebrows (supercilia), eyelashes (cilia), and bristles at the entrance to the anterior nares (vibrissm). The straightness or curliness of hairs depends upon the form of their shaft. In the first instance, the transverse section of the latter is round ; in the second, oval, or even reniform. Hairs are found either singly, in pairs, or small groups. The oblique direction of the follicles also brings Avith it great variety of position in the various localities (Eschricht). In the several parts of the body the number of hairs likewise is found to vary considerably, so that, while on the scalp 293 have been counted to the square inch, the same super- ficial extent of the chin has only shown 39, and on the anterior aspect of the leg, 13 (Withof). It is hardly necessary to remark that, together with this variation, many individual differences present themselves. The structures we are engaged in considering are remarkable for their great strength and elasticity. They will support a considerable weight without breaking, and return almost to their original length again on removal of the extending force, if the latter have not been altogether too great. Owing to their dry and horny composition, they belong to the most durable of all the tissues of the body; witness the hairs of mummies. They absorb moisture greedily from without—in the first place, aqueous 396 MANUAL OF HISTOLOGY. vapour from the atmosphere ; and again, through the bulb, from the fluids of the neighbourhood. It is upon this property that the interchange of matters Avhich takes place in hairs is dependent. The latter appears to be by no means inconsiderable, as we may infer from the rapidity with which hairs in some instances turn grey. The appearance of air within the medulla folloAVs upon a process of drying up which takes place there. The shaft of the hair, however, is also saturated with the oil of the sebaceous secretions. As Henle very properly remarks, we may recognise ♦ the physiological condition of the skin from the state of the hairs ; their brittleness on the one hand, and softness, pliancy, and glossy appearance on the other. The growth and the nutrition of these structures takes place in a manner exactly simdar to that of the nails (p. 164). Multiplication of cells takes place by segmentation at the loAvest and softest part of the bulb, kept up by supply of material through the blood-vessels of the follicle, and more directly through those of the papilla?. Aud just as the growth of nails can be accelerated by paring the free edge, so does cut- ting of the ends of the structures in question favour their rapid produc- tion, as is seen in the beard after frequent shaving. On the other hand, when both these tissues are left in the natural state, uncut, they seem eventually to reach a point at which they cease to grow. We have already seen that the nail may be completely reproduced so long as its bed remains uninjured. The same is the case with the hair if its follicle remain intact. This regeneration is called into play extensively during the earlier periods of life; and even later on, renewal takes place, to supply the loss of large numbers of hairs which is sustained by the healthiest body yearly, owing to disappearance of their roots. The hair destined to be cast off is seen to be swollen at its lower end, and to be destitute of the earlier excavation for the papilla. This is the "hair-knob" (Haar- kolben) of Henle. Later on, loosening from the papilla, the whole hair splits, and breaks up into a number of shreds, and becomes like a brush. Pincus estimated the average daily loss of hairs from the heads of young men to be, under normal conditions, from 38 to 108. The phenomena of growth observed accurately by Berthold in relation to the nails have also been studied as regards the hairs. The latter grow more rapidly at night than during the day, and in the warmer than in the cold seasons of the year. They are also produced more quickly when frequently cut. Thus the hairs of the beard when shaved every twelve hours, show a growth in the year of 12"; when cut every twenty-four hours, only 7|"; and when shaved every thirty-six hours, only 6§". §218. From the extensive researches of Valentin first, and then Koelliker, we learn that the first rudiments of the hairs are formed in the human embryo at the end of the third and beginning of the fourth month, appear- ing first on the forehead and eyebrows (fig. 395). Here we find nodulated or mamillated aggregations of cells (m) 00451 mm. in length, belonging to the rete mucosum (b), which sink gradually into the cutis by a process of proliferation, pushing the adjacent part of the latter before them. These cells increase rapidly in number, so that the collection soon becomes larger and more flask-shaped. Around the latter there may now be remarked a thin homogeneous transparent membrane (i), probably the hyaline internal layer of the future follicle, about which the corium is TISSUES OF THE BODY. 397 gradually transformed into the peripheral portion of the follicle. Up to this stage the development of sweat glands and hairs is identical (§ 200). Although at the commencement the whole aggregation of cells appears solid, and of the same nature throughout, a distinction soon makes itself evident between an axial and peripheral ^ ___ iimi j__ portion. From the first is formed the &.....-j^BB^. "5S3IB hair and its internal root-sheath, from the ^W^P^ second the external sheath. The cells /MmiM of the last-named stratum are elongated S^^SaSi transversely, Avhile those of the axial **'"^m^wl * portion of the rudimentary hair in- \jB||^" crease in a longitudinal direction. This is the state of the parts in the eighteenth m wppk of intrfl-ntpn'TiP lifp at wriir-h Httip Fi£- 395.—First rudiments of a hair from the weeK oi lntra-utenne me, at wnicn time human embl.y0 at sixteen weeks, a% b< the agglomeration of Cells has attained layers of the cuticle; m, m, cells of the a length of 0*226-0*0451 mm. rudimentary hair; i, hyaline envelope. Soon after, a new division in this internally someAvhat club-shaped mass, —broad beloAv, and more or less pointed above,—commences; the outer layer, namely, with its cells, is transformed into the clear transparent internal root-sheath, Avhilst the axial part, Avhich becomes the bulb and shaft of the hair, remains dark. At this period, also, the papilla may be clearly seen. The true hair thus commenced is at first short, and surrounded by a very strong internal root-sheath, but Avithout any recognisable medullary substance. It then gradually increases in length, passes between the undermost cells of the epidermis, and perforates the latter either immedi- ately or after turning on itself, and taking an oblique course for a certain distance. The other hairs are developed in a manner exactly similar, but later. At the end of the sixth or commencement of the seventh month, most of them have made their appearance through the epidermis. The hairs, so appearing by perforation of the cuticle, are thin and light-coloured. In regard to the regeneration of hairs it must be remembered that many of the downy ones are cast off during infra-uterine life, and become mixed up Avith the waters of the ovum. After birth, however, this change of hairs increases in amount, the new appearing in the place of the old. Evert at an advanced age this regeneration does not cease in man. Among the mammals, as is well known, a very extensive reneAval of hair takes place periodically. In regard, however, to these processes there still exists considerable difference of opinion. It Avas Koelliker Avho first observed the regeneration of hairs in the eyelids of the infant (fig. 396). From bis statements it will be seen, in the first place, that the bulb of the old hair separates from its papilla, from which the rudiments of a neAv structure are produced in the form of a conical mass (A, m). Above this, consequently, lies the loosened hair (de), horny down to^. the very bulb. This rudimentary structure (B) is transformed into hair bulb (/) and shaft (bh), Avith inner root-sheath (g), in a manner pre- cisely similar to that we have already seen in the formation of hair in the embryo. The inner root-sheath of the old hair disappears from the com- mencement, and the new-comer drives its point by the side of the first, which is displaced, through the outlet of the follicle occupying the whole of the latter as soon as its former occupant falls out. Koelliker has also 398 MANUAL OF HISTOLOGY. stated that with this process there takes place, farther, a growth downwards of the follicle into the cutis, but this view is combated by other observers This mode of explaining the regeneration of the hair from the old papilla, from Avhat we and others have seen, is, we consider, quite correct. Whether it includes all that occurs at the time of change, is another question. According to Slieda's state- ments, on the other hand, the ' papdlee of those hairs which are about to be cast off degenerate. A residue of those indifferent formative cells, hoAvever, from Avhich, as we have seen, the specific tissue ofthe hair is formed (§ 214), remains behind in the fundus of the follicle, commences then to groAv downwards into the cutis, and becomes cupped by- pressing down upon a new papilla rising and formed from the latter. From this cellular mass covering the papilla the new hair takes its origin. That the whole structure—fol- licle, outer root-sheath, and hair— may be newly formed under normal conditions, at a later period of life, appears probable; occurrence to be the rule in the This requires, however, more care- Fig. 396.—From the eyelid of a child of a year old, showing new formation of hairs at the bottom of the sacs. A, early, B, later stage of development, a, external, g, internal root-sheath; d, bulb, and «, shaft of the old hair; i, sebaceous follicles; k, ducts of sweat-glands; c, funnel-shaped pit at base of the new rudimentary hair which is seen at m, fig. A, to be still quite homogeneous; whilst in fig. B the bulb /, stem 6, and point h, may be recognised. indeed, Wertheim believes such an change of hair in the human being. ful investigation. Pathological neoplasis of hairs and follicles, on the other hand, does occur Avithout doubt under the most extraordinary circumstances. Hairs are met with on mucous membranes, but only extremely rarely ; again, on the internal surface of follicular tumours or cysts in the skin and ovaries, in which case the wall of the cyst has been found to have assumed a similar constitution to the outer skin, and to contain not only hair and sebaceous glands, but also sweat glands. Transplantation of hairs, together with their follicles, succeeds likewise. Search among the follicles often brings us into contact Avith hairs destined to fall out. These have parted from the papilla upon which young cells and pigmentary matters are to be seen. The appearance of their roots is also altered; they seem as though broken up into fibres resembling in figure the end of a broom, and are, like the whole hair, paler and free of pigment. Beneath these the root-sheaths and follicles are narrowed for a greater or less distance, and in the latter small newly- formed hairs may be met with. §219. The tissues we have been engaged in describing up to the present, are combined in various ways, and under great variety of outward form, to TISSUES OF THE BODY. 399 produce the several organs and apparatuses of the body. These organs, Avhose performances are dependent on the individual qualities of the various tissues of Avhich they are composed, present far greater difficulties, as regards their classification, than the tissues themselves (§ 64),—the more so, as we are unable accurately to define what is precisely meant by an organ. If Ave compare the many apparatuses of the body, we find the greatest differences existing as regards their construction. Some of them are formed in the simplest manner of one single tissue, as, for instance, the nails, the lens, the \dtreous humour. Their performances, in such cases, may also agree with the physiological energy of the tissue. Other organs, however, are combinations of several, of many, nay, even of most, of the tissues of the body. It will suffice to point, by way of example, to the organs of vision. Thus, here, as in the classification of tissues, the systematic worth of the terms simple and compound seem to recommend them for use. This principle of division, however, can be by no means so strictly adhered to here, owing to the multitude of organs, as Avas the case in dealing Avith the tissues. It is a common mode of classification among anatomists to group the organs of the body in particular systems. By this we understand the arrangements of parts together, which are found to be identical or similar as regards the finer composition of their tissues. Thus the present divisions into nerves, muscles, osseous, and vascular systems have been arrived at. We also speak, however, of a digestive and generative system, Avhere this similarity of texture in the various parts making up the whole by no means exists. Thus in the many manuals Avhich treat of these subjects the greatest differences as regards classification may be observed. It may be found most expedient, then, if we base the third section of this Avork upon the principle of physiological classification, and make use of the old division of organs, into those which take part in the vegetative occurrences of the body, and those belonging to the animal side of life. It cannot be denied, however, that this classification will not everywhere hold good; for in the Avonderful linking of parts one with another there occur many intermediate forms. Thus nerves and muscles make their appearance in apparatuses belonging to the vege- tative sphere, blood and lymphatic vessels, and glands in animal organs, and so on. Starting from this point, then, we come to another mode of grouping parts, namely into apparatuses, that is, a combination of a number of organs for the carrying out of some one physiological purpose. A system and apparatus may correspond, as in bony, muscular, and nervous portions of the body, but do not necessarily. Thus from one point of view there is such a thing as a digestive and respiratory apparatus, but not a diges- tive and respiratory system. The following is our classification of organs:— A. Belonging to the Vegetative Group. 1. Circulatory apparatus. 2. Respiratory apparatus. 3. Digestive apparatus. 4. Urinary apparatus. 5. Generative apparatus. 400 MANUAL OF HISTOLOGY. B. Belonging to the Animal Group. 6. Bony apparatus or system. 7. Muscular apparatus or system. 8. Nervous apparatus or system. 9. Sensory apparatus. Having been obliged, in speaking of the different tissues, to refer fre- quently to their arrangement in the formation of various organs, or their constitution Avithin composite apparatuses, the discussion of this third part, or Topographical Histology, will be very irregular as regards the several parts. The chief object to be kept in view will be the description of the finer structure of organs, with reference to that, in the microscopical relations of the same which could not before be brought under notice. m. 0KGANS OF THE BODY. I III. THE ORGANS OF THE BODY. A. Organs of the Vegetative Group. 1. Circulatory Apparatus. § 220. As Ave have already considered the blood and lymphatic vessels in tho second part of our work (§§ 201-211), we shall here be engaged merely with gleanings from what has been previously referred to. Thus we have to describe the heart, the lymphatic glands and lymphatic organs, with the spleen, as Avell as the remainder of the so-called blood-vascular glands. The heart—the muscular central organ of the circulatory system— consists of the pericardium, a serous sac (which has been previously referred to, p. 226) of muscle, and of the so-called endocardium. Tho latter is analogous to the T. intima of larger vessels (§ 204), while the fleshy mass of the organ corresponds to the mus- cular layers of the latter. Many modifi- cations, however, are apparent. The pericardium corresponds in its texture to many of the true serous sacs. It presents for consideration a thick pari- etal and thin visceral portion. The latter is connected with the fleshy mass of the organ by means of that connective-tissue known as subserous, and shows espe- cially in the grooves of the heart, but at times also over nearly its whole surface, collections of fat cells (p. 198). The vessels of this structure have nothing special about them, and the nerves of the parietal layer are supplied, accord- to Luschka, by the right vagus (ramus recurrens) and phrenic. The epithelium has been already dealt with at p. 139, Fig 397._Muscle.fibres Ir„m the heart, and the fluid Contents Of the Sac at p. after Schweiyger Seidel. To the right the non boundaries of the cells and the nuclei ■""U. are to be seen. We have likeAvise considered the stri- ated muscle of this involuntarily acting organ while speaking of muscle generally at p. 292. The connection of the reticularly united muscular fibres one with another (fig. 397) is very peculiar. They are not, as in other striped 404 MANUAL OF HISTOLOGY. muscle, collected into bundles, excepting the trabeculce carneoe, m.pectinati and papillares. The single fibres lie rather closely crowded side by side, held together by a small quantity of connective-tissue. As is Avell known, the strength of the fleshy mass varies much in the different divisions of the heart. It is most massive in the left ventricle, thin in the two auricles, and weakest in the right of these. The course Avhich the fibres take is also very complicated, for Avhich reason we shall confine ourselves to only a few of the chief points of interest as regards it. The course of the fibres of the heart, which is different in the auricles and ventricles, may be divided into longitudinal and circular. This distinction, however, can only be made with accuracy as regards the auricles, and not the ventricles. It is a remarkable fact, further, that some of the muscular fibres are common to the two auricles, and another to the two ventricles, while each of these four parts possesses also its special fibres. The starting-points of the fibres of the heart are usually held to be the two annular masses of fibres which encircle the ostia venosa of the ventricles, known as the annuli fibro-cartilaginei. They consist of very strong connective-tissue, with very delicate elastic fibres. Sometimes their tissue assumes a similar appearance to that of the perichondrium at its transition into true cartilaginous tissue. From these rings the fibres take their origin, and return, after travelling round the cavities of the organ, to be inserted into them again, thus forming loops. In consequence of this, both auricles and ventricles must contract towards these points, the bases of the ventricles, during systole of the organ. In the auricles we encounter in the first place, as most internal layer, bundles of fibres springing from the ostium venosum, and forming a series of loops, which arch over the cavity, producing a kind of dome. From their peculiar development in the right auricle they give rise to the m.- pectinati. This layer is enveloped by another stronger one, formed of circular fibres, which is in the first place distinct for each of the auricles, and then specially developed on the anterior aspect of the organ, it includes both of them in common. Finally, surrounding the openings of the veins we find circular fibres, continued to a certain distance over the walls of these vessels. The arrangement of the fibres of the ventricles, however, is more complex. In the first place, it may be remarked that the left ventricle possesses a special set of fibres. The right has likewise its own, which are, however, so arranged as to strengthen the muscular mass of the left, being produced into it. Finally, fleshy fibres are to be seen, which' starting from the left ventricle and returning to the same, surround in their course the right cavity in loops. It may be remarked, namely, that from the fibrous ring of the left side and from the aorta also, in the whole circumference of the ventricle a number of longitudinal fleshy fibres take their origin, which descend 'on the one wall in its outer portion, and bending round at the apex of the heart return m the inner surface of the opposite wall to the annulus fibro- cartilaginous. Owing to the oblique course of these fibres they cross each other at the apex of the left ventricle, forming there the so-called vortex, of the heart. In the right ventricle, likewise, we meet with an origin of fibres from the annulus fibro-cartilagineus. There one limb of the loop pursues a course in a similar manner down to the apex of the ricdit ORGANS OF THE BODY. 4Q5 cavity, but passes then, not into the opposite wall of the same, but into the wall of the left ventricle, arriving eventually at the left fibrous ring, where it terminates. Besides this peculiar arrangement of the fibres, which is, however, on the Avhole a longitudinal one, there is also a circular set. This takes its rise from the left annulus, and surrounds the wall of the left ventricle in figures of eight, while other fleshy bundles arising in the same region envelope the right chamber in simple loops. These different masses of fibres lie betAveen the longitudinal. From the right annulus also, though in much smaller number, similar fibres take their rise, encircling the wall of the left ventricle in the same kind of simple loops. Finally, we have another set of circidar fibres, which, springing from the right annulus, return to be inserted into the same„ encircling in their course the conus arteriosus. The muscuke papillares are formed both from the longitudinal and trans- verse fibres. In conclusion, we must devote a few lines to those peculiar structures, discovered in the year 1845 in the hearts of horses, coavs, sheep, and pigs, which have been named, in honour of the discoverer, the fibres of Purkinje. These present themselves as flat grey jelly-like threads, spread out in a reticular manner, immediately under the endocardium, on the internal surface of the ventricles. They penetrate further into the musculae papdlares, and stretch across various depressions in the walls of the heart. Purkinje's fibres (which were subsequently found to exist in the hearts of deer and goats) are structures Avhose significance is far from being understood as yet. We may see that they consist of rows of round or polygonal nucleated bodies, ranged side by side, or one over the other, which have received the name of " the granules." Between these is noticed a plexiform or reticulated arrangement of the so-called "interstitial substance." The latter consists of thinner or thicker fibres of striped muscle, which can be followed into the substance of the heart. Those cell-like bodies which lie in the interstices also frequently present a transverse and longitudinal striation, and may unite finally with the surrounding striped netAvork to form stronger muscular fibres. For our own part Ave look upon the whole as a strange complicated interlacement of cardial or endocardial muscle fibres, which have remained stationary at an embryonic stage of development. We refer the reader to the genesis Of the latter (§ 172). §221. All the cavities of the heart, with their inequalities and projections, are clothed with an endocardium of varying thickness. This structure is thinnest in the ventricles, where it is presented to us in the form of a delicate membrane, and thickest in the atrium sinistrum, where it forms a tough lining. It consists of several layers. As a substratum may be recognised an elastic lamina Avith abundant elastic fibrous networks, and corresponding poorness in connective-tissue. Internally appears a specially dense lamella of an elastic network supporting a coating of simple endothelium (p. 139). The external layer contains, besides, in the ventricles, smooth and transverse muscle fibres; but in the auricles only a feAV scattered contractile fibre-cells are to be found (Schweigger-Seidel). 406 MANUAL OF HISTOLOGY. The valves betAveen the auricles and ventricles (valvule* tncuspidales and mitrales) are duplicatures of endocardium, with a strong middle layer of fibrous tissue, derived principally from the fibres of the annulus fibro- cartilagineus, and expansions of the tendons of the muscuh papdlares On one aspect they are clothed with the strong endocardium of the auricle, on the other by the thinner of the ventricle. Under the first of these endocardia muscular bands are prolonged into the valves from the muscular substance of the auricle penetrating to various depths (Gussenbaur). Finally, the Avhole is covered Avith simple endothelium. Ihe semi- lunar valves also of the arteries have a similar structure, except that the middle layer is thinner. The blood-vessels of the heart present in its muscular substance the most typical form of the elongated'mesh-work (p. 370). Several capil- laries pass immediately and together into one strong venous root. The ready outflowing of the blood is thus better provided for than elsewhere. The endocardium is only provided Avith vessels in its undermost connec- tive-tissue layer. A feAV may also be seen in the auriculo-ventricular valves, but none in the semdunar (Gerlach). The heart is supplied with lymphatic vessels in considerable number, and according to Eberth, Belajeff, Wedl. The tAvo leaves of the pericardium, as well as the endocardium, contain dense networks of coarser or finer trunks. In the interior of the auricles they appear more scanty than in the ventricles. In the chordae tendinese, on the other hand, they are not to be found, and in the semilunar and auriculo-ventricular valves are only present in smad number. The fleshy substance of the heart does not appear to be so richly supplied with them as Avas formerly supposed by Luschka. The nerves of the heart have their origin from the cardiac plexus, which is itself made up of branches from the vagus and sympathetic. The course of the numerous nervous stems is alongside of the blood- vessels until they spread out in the auricles and ventricles. The auricles are poorer in nerves than the ventricles, of Avhich the left is the most richly supplied. The nerves of the heart appear more or less grey, and consist of fine medullated tubes with an intermixture of Remak's fibres. They terminate for the greater part in the muscle, Avhile some of them may be traced into the endocardium. All efforts to elucidate the mode of ultimate termination here have hitherto proved futile in man and the mammalia generally. The occurrence of numerous microscopically small ganglia is also pecuhar. The latter appear on the nerves imbedded in the substance of the heart, especially in the neighbourhood of the trans- verse groove and septum ventriculorum. Physiology, as is well known, has brought to light the interesting fact that these two kinds of fibre elements are entirely different in function. Whilst the sympathetic, namely, preside over the contraction of the muscle, having their chief centres of energy in the ganglia just referred to, so that the heart continues to pulsate after removal; the vagus fila- ments exercises a completely opposite influence, causing, when stimulated, an interruption to the motor poAver of the sympathetic elements, and to such an extent also that the heart comes to a standstill in a condition of diastole (E. Weber). It is possible that the fibres of the vagus may terminate in the cardiac ganglia, i.e., in their cells. Regarding the composition of the muscle of the heart, vide chemistry of ORGANS OF THE BODY. 407 muscular tissue (§ 170, p. 295). The occurrence in it alone of inosite is a fact of great interest. The structure of the arteries and veins has been already discussed in §§ 203 and 204, that of the capillaries in §§ 201 and 202. We now turn to the consideration of those peculiar bean-shaped and very vascular organs, the lymphatic glands or lymph-nodes, which occur in the bodies of the higher vertebrates, interrupting the course of the larger absorbent vessels. They are met with in greatest number on the lymphatic trunks of the intestines, and at those points where superficial and deeper sets of vessels join. It not unfrequently comes to pass that one single vessel is in this way interrupted over and over again by such nodes, and it is probable that every trunk in its course from the peri- phery to the ductus thoracicus has at least one such. In those lymph- nodes, which are not very minute (fig. 380, a), we usually find several lymphatic tAvigs penetrating into their interior from the convex border. These are the vasa afferentia (f, /). From the other side either one or more vessels (in the first case of greater calibre), make their exit, known as the vasa efferentia (A). This takes place as a rule at a point where a kind of depression may be observed, and where the larger blood-vessels enter the organ. This spot, when the depression is present, is named the hilus (h). It is entirely absent, however, in many glands. The internal arrangement of the lymph-nodes is a point most difficult to determine, and it is only very recently that any satisfactory insight has been gained into their minute structure. We learn, besides, from recent observations, that the organs in question display consi- derable variety, both as re- gards volume, compared with the size of the mam- mal body, and also their locality; so that the struc- ture, for instance, of a large lymph-node from an ox, and a small one from a rabbit or Guinea-pig, exhibits great difference. Were this axiom allowed its due Aveight, we should be -spared many unprofit- able controversies. In those lymph-nodes Avhich are not altogether too small Ave can distinguish a reddish grey cor- tical portion, consisting of round bodies, the follicles (m the mesenteric glands of a dog. a, capillary, b, re- ticular connective sub- stance forming tlie tube. 412 MANUAL OF HISTOLOGY. 403, 404). These vary extremely in thickness, besides which one and the same tube may exhibit at different parts of its course very different dia- meters. Fine lymph tubes may measure 00361 mm., or even considerably less, across, whilst others show a thickness tAvo or three times as great. Even in the smaller mammals some may be met with of 0*0902- 0*1263 mm. in diameter. In the large lymph-nodes of the ox tubular elements of the medullary substance maybeencountered present- ing a still greater diameter. If we now pass on to the structure of the lymph- tubes, Ave have the most striking picture presented to us on filling the blood- vessels artificially; all the lymph-tubes, namely, are traversed by blood-vessels, so that they appear like lymph-sheaths around the latter. According to their strength, Ave find the axis occupied by either an arterial twig, a capillary (figs. 402, a; 403), or a small venous branch. If, as is the case in larger animals, the lymph tubes are of considerable thickness, their vascular system is more complicated, as is seen in fig. 404, a. Here also an arterial or venous twig passes through the axis, Avhile the peripheral portion is traversed by interlacing capil- laries belonging to the axial vessel and forming elongated meshes. The tissue of the lymph-tubes is again reticular connective substance; a cellular or banded network (fig. 402, b), which surrounds the blood-vessels and takes the place of an adventitia. In thick lymph-tubes also the reticular character may be recognised in their in- terior. The surface likeAvise is often ob- served with the greatest distinctness to have mesh-like slits. In finer tubes, as also in those of the smaller animals, such as the rabbit (fig. 403, a, b), the external surface may become more or less membraneous and homogeneous, resembling a hyaline glandular Fig. 403.—Lymph tubes (a, a) from the medullary portion of the pancreas Asellii of the rabbit, with simple vessels and their branches, 6, 6. Between them is to be seen a strongly stretched cellular network c. Fig. 404.—From the medullary substance of the inguinal gland of the ox (after His)\ a, Lymph-tube with its com- plicated system of vessels; c, portion of another; d, septa; 6. retinacuia stretched between the tube and the septa. ORGANS OF THE BODY. 413 tube to a certain ex'ent. This variety, in the demarcation of the forma- tions in question, is explained by the changeable nature of reticular connective substance. AVe are now met by the questions, whence come these lymph tubes 1 what is their origin, and what becomes of them ? It is comparatively easy to recognise the origin of the lymph-tubes from the follicles (fig. 405). They spring from the under surface of the latter (d, e), and it ap- pears ahvays several of them together. The sus- tentacular matter of the follicle becomes the band- ed netAvork of the lymph- tube, and the blood-vessel of the latter enters the follicle at this point. At this under surface the septal system is very fre- quently extremely imper- fect; comp. fig. 401. Passing on now to the consideration of the se- cond question, namely, What becomes of the lymph tubes 1 nothing would seem more natural —bearing in mind the parallelism of the latter with the blood-vessels— than that they should converge towards the hilus of the organ, forming eventually by their confluence, and on separating from the latter, the vas efferens; and, indeed, this utterly incorrect vieAv of the state of parts has been put forward by some. More accu- rate observation, however, of the medullary portion of the gland convinces us that no such thing takes place, but that the net- work of the tubes, just as it took its rise on the one hand from follicles, so is it on the other hand continuous (subject to many variations certainly) Avith other follicles (fig. 401). Consequently, in this highly developed reticular arrangement of the lymph tubes of the medullary substance, Ave have nothing but a very complicated system of intercommunications between the follicles of the lymphatic nodes. Ilecognising uoav the medullary mass as a netAvork of lymph-tubes, we must, of course, expect to meet with a correspond- ing system of interstices. Throughout these lacuna** (sometimes in the greater part of them (fig. 388, 6), sometimes only in some fe*w) the system of connective-tissue septa Avith which we have been already made ac- quainted extends. But, as was before observed, in regard to the parti Fig 405. Fig. 406. 414 MANUAL OF HISTOLOGY. tions in the cortical portion, the septa do not come into contact with the lymphoid substance here either. On the contrary, we find,—as in the first case, so here also,—the lymph-tubes and septa, or, where the latter are absent, the lymph-tubes alone, separated from one another by a nar- roAver or broader interval analogous to the investing space of the follicle. There now remains for consideration the contents of these reticulated passages of the medullary substance. Here, as in the investing space of the follicles, a certain number of lymph-corpuscles are to be found, which may be removed Avith a brush. Besides these, we observe that a con- nective-tissue network, with a varying amount of nodal points, nuclei, and processes, occupies the passages with wide straggling meshes (fig. 406, b; 405, I). Springing on the one hand, from the septa of the gland, its fibres sink on the other into the reticular tissue of the lymph-tube, or, where there are no septa, connect one lymph-tube with another. Not unfrequently in the mesenteric glands, as for instance in the pancreas Asellii of the rabbit, some very interesting points in regard to the cellular network occupying the interstices of the medullary substance may be observed (fig. 407, c). The bodies of the cells appear tense and sAvollen : they have, moreover, no membrane. Their processes or ramifications are like- Avise thickened and broad. Within both the bodies and their processes, be- sides soft-looking nuclei, isolated lymph corpuscles are to be seen ( W. Miiller, Frey), which may have come there either by im- migration or possibly by generation on the spot. The possibility of this latter alternative remains, however, still a matter of uncertainty. If we follow up the reti- cular interstices of the medullary substance to the boundary of the latter, we have no difficulty in re- cognising the fact (especi- ally if we carry our eye that they lead into the investing spaces of the foiKrtjf ^$**«™) From all this we learn that the lymph-nodes are formed of a system of cavities (imperfectly bounded by septa) which are occupied by Whoid matter-in the cortical portion by the follicles, and in the medulW by the lymph-tubes-but always so arranged that the lymphoid substance does not come into contact with the fibrous septal system Thus ^ have both a series of spaces, encasing, as it were, the follicfos, (invests Fig. 407. spaces), and a system of intercommunicatim passages enveloping the ORGANS OF THE BODY. 415 lymph-tubes (the lymph-passages of the medullary portion. Throughout this extremely complicated cavity in the larger lymph-glands, then, a net- Avork of fibrous bands and cells extends, springing from the lymphoid substance on the one hand, and is attached to the septa on the other, holding the whole lymphoid sustentacular matter in a tense condition. We must noAv turn to the more active portions of our organ, namely, the blood and lymph streams. §225. Artificial injection of the blood-vessels of lymph-nodes is a matter of but slight difficulty. It shoAvs us that the organs in question receive their supply of blood from two different sources of unequal importance. The larger arterial tAvigs in the first place pass into the septa and glandular tissue through the hilus without exception, while the smaller branches penetrate through the capsule into the interior. The last mode of supply, however, is probably not always present, though others are wrong who assert that it does not exist at all. Passing through the hilus in the first place then, one or several small arterial trunks are seen which give off their first branches while within the connective-tissue situated here. With the connective-tissue a small number of these branches pass into the system of septa Avithin, ramifying Avith further division towards the periphery. Most of the arterial twigs, however, penetrate into the lymph-tubes of the medullary substance, and pursue their way within the offsets of the latter. Among the smaller lymph-tubes, such as those of the pancreas Asellii of the rabbit and Guinea pig, as well as the mesenteric glands of man, each of the former contains, as a rule, but one single axial vessel, either a small artery- vein or capillary. In lymph-tubes of greater diameter several of these may be met Avith, or, as is the case in the inguinal glands of man and lymph-nodes of the ox, these elements of the medullary substance contain within them a thick arterial or venous axial vessel, and a long-meshed capillary network around it (fig. 406), Avhose tubules have a medium diameter of 0*0046-0*0090 mm., and form a most delicate interlacement about the central vessel. Passing from the more external lymph-tubes, these twigs, together Avith their capillaries, enter the follicles, and occupy a considerable portion of its space, terminating eventually in a very loose and rather irregular capillary network. The latter exhibits at the periphery of the follicle where it is most highly developed as a rule, numbers of loops on the tubes from the union of which the venous radicals take their origin, Avhich lie more internally. These, on leaving the follicles, penetrate into the lymph-tubes, and return (imitating the arrangement of the arteries) through these to the hilus. The second source of supply of blood is the capsule of the lymph-node which is traversed by arterial venous and capillary vessels. The first of these appear in the bases of the interfollicular partitions as horizontal twigs, Avhich divide finally into finer branches encircling the various follicles. The veins of the capsular tissue have a similar course. Internally the greater number of these capsular vessels sink into the septa, communicating there with others coming from the hilus. Other tAvigs (rarely arterial or venous, but usually capillary) enter the follicular tissue itself, taking a course through the stronger retinacuia of the investing space or through the partitions. We shall find later on that other organs, such as the spleen, liver, and 416 MANUAL OF HISTOLOGY. kidneys, exhibit a similar connection betAveen the vessels of the paren- chyma and capsule. For the recognition of the course of the lymph, also, we require the aid of artificial injection. This may be successfully performed through the vas afferens, though not easily. On the other hand, it may be very easily effected by Hyrtl's method of puncture beneath the capsule. The true course of the lymph through the gland Avas, hoAvever, first ascertained by myself in the year 1860, and shortly aftenvards by His. The afferent lymphatic vessels (fig. 408, /, /) euter the organ either singly or, as is the case Avith larger nodes, in greater number. Their walls are thin, and they exhibit considerable variety of diameter and richness in valves. There may also be one or several efferent vessels leaving the glands. They have a similar structure to the last. Their point of exit may be a depression like the hilus, although not necessarily, so that the distinguishing of afferent and efferent vessels from one another is not always an easy matter. If Ave cautiously force in some injecting fluid through one of the vessels leading into the organ, the first portion to fill is a series of spaces under the capsule, closely communicating with one another, and surrounding the follicle: this is effected with great ease. Perpendicular sections show that the fluid penetrates also into the interior by keeping along the sides of the follicles, and in the middle of the stream the banded network of the interfollicular septa is seen distinctly. AVhat is here produced artificially is effected by nature also. A few hours after a meal of fatty food, the cortical portion of the mesenteric glands is filled by Avhite chyle in a manner precisely similar. It requires but a slight acquaintance Avith the lymph-nodes to convince one's self that the injection fluid, in fact, on first entering the organ, finds its way into the investing spaces of the follicle, and, filling these, occupies those circular netAvorks on the surface of the latter which have been already mentioned above as being 0*0162-0*0323-0*0483 mm. in breadth. Close inspection sIioavs farther that the afferent lymphatic vessel, from that point at Avhich it enters the capsule, loses its independent Avail by the fusion of the outer layers of the latter with the connective-tissue of the capsule. In this Avay it opens into the investing space, either in the form of a simple or branched pas- sage. Thus the effects of injection are easily ex- plained. It may be mentioned, as a modification of this ar- rangement, that the afferent lymphatic tubes sometimes ,, . . . „ „. , nrst pass for a certain dis- tance through the interfollicular partitions before opening into the lym- phatic spaces of the gland. Let us bear in mind farther that the investing spaces of the or^an are immediately continuous with the network of interstices of the medul- Fig.408. ORGANS OF THE BODY. 417 sa- lary substance (§ 224), so that there can be no doubt as to the farther course of the injection fluid: it fills namely this network of lymph pas- sages also, while the lymph tubes of the medullary substance remain colourless so long as only slight pressure is used. From the mode of termination of the injection Ave perceive that the vas efferens must take its rise from the passages of the medullary portion of the gland, in that it is at last filled by the fluid employed. It is also possible at times to drive the liquid back through the vas efferens into the lymph node by overcoming the opposition of the valves. Retrograde injections of this kind impel the matter used first into the reticulated passages between the lymph-tubes of the medulla, and from thence further on into the investing spaces of the foUicles. The confluence of these medullary lymph streams, however, to form a branch of the vas efferens is a point very difficult of detection (fig. 409). The latter vessel which leads into the connective-tissue at the hilus undergoes there .further division into branches, as has been already remarked. These may vary greatly according to the size of the gland, and the greater or less development of the fibrous nucleus of the latter. En- closed within the partitions of the medulla, the last branches of the vas efferens (e) are observed to course along in the form of tubes of various calibre, whose Avails are, as a rule, fused with the surrounding connective-tissue (/). Finally, on penetrating further into the gland we observe that the partitions Avhich contain such ramifications of the vas efferens become subdivided more and more, forming series of diverging bands, so that the lymph stream is no longer enclosed Avithin an envelope, and exhibits all the reticular characters and irregular limitations (d) charac- teristic of the hollow cavities of the medulla. In fact, there can be no doubt that we have before us the origin of the vas efferens from the cavernous portion of the medulla of the gland. It may be remarked, further, that the vasa efferentia on their exit from the lymph nodes present much variety of appearance, depending upon the size of the organ and the development of the connective-tissue nucleus in the neighbourhood of the hilus. Thus in the hilus of the large mesenteric glands of the ox a regular plexus of peculiar, very tortuous, and knotted vessels has been seen by Koelliker, and Teichmann also gives drawings of exceedingly complicated vasa efferentia. From the foregoing description, then, the following conclusions may be drawn. The vessel leading into the gland pierces its capsule in the form of a canal, and opens into the investing spaces of the follicle. These lead then into the lymph passages of the medullary portion, from the confluence of Avhich the radicals of the vasa efferentia enclosed within the substance of the converging partitions are formed. From this Ave see that really independent lymphatic vessels do not Fig. 409.—From the medullary substance of an inguinal gland of a large dog. a, lymph tubes; b, empty reticulated passages of the medulla; c, the same filled ; d, tran- sition into the commencement of a twig of the vas efferens; e, the latter coursing along within a fibrous septum //. 418 MANUAL OF HISTOLOGY. Fig. 410. exist in the glands in question, and that the views entertained to the opposite effect are incorrect, as those of Teichmann, for instance. On the other hand, that older and so Avidely held view to Avhich Ave our- selves subscribed for many years can no longer be supported in its integrity, namely, that only lacunar circulation takes place Avithin the lymph nodes. The lymphatic canals, namely, traversing the capsule are, as we may easily convince ourselves, lined with peculiar flat epithelium-like cells (fig. 410), already dealt with in considering the vascular system (§ 208). The investing spaces are likewise lined in the same manner, not only on the surfaces of the septa and the retinacuia con- nected with them, but those of the follicles themselves (His). It is still a matter of uncer- tainty whether the lymph passages of the medulla possess a similar lining or no. This matter calls, at all events, for more accurate investigation; for we find— not alone after artificial injection, but also from the stream of lymph pass- ing through—that small granules of colouring matters or fats penetrate from the periphery towards the centre of the follicles, and also into the lymph tubes. They are also seen in the cellular network passing across the interstices of the medullary portion of the gland. We know, farther, that the lymph of the afferent vessels is not unfrequently poorer in cells than that Avhich leaves the organ. From this fact Ave may infer that from the substance of the gland lymph corpuscles are yielded to the passing fluid. The lively change of shape of the cells of the latter, and consequent power of change of locality (§ 40), as Avell as the trellis-like surface of both follicle and lymph tube—the fact, finally, which has been already considered in a previous section, that cellular networks containing lymph corpuscles are observed in the passages of the medulla,—all these point to the probability of such an addition being here made to the fluid. Our knowledge of the nervous supply of the lymph glands is at present extremely scanty. Some fine nervous twigs have been observed by Koel- liker, in the larger nodes of the human body, to pass in with the arteries into the medullary portion; beside which Remak's pale nerve fibres have also been observed in the glands of the ox. Remarks -1. No doubt can any longer prevail as to the perviousness of the lymph glands to small solid granules. And although, after tatooing, molecules of pigmentary matter are laid down in these organs, the fact can be explained in a manner quite reconcilable to this view. Every one who has ever injected lymph nodes wS S,yftannl? ^ftter' anT aft™rds ^ayed to brush it out, knows very well with what tenacity the granules cling to parts of the surface of the investing space That ymphoid cells possess the power of taking up molecules of pigmentary matter into their bodies has already been remarked at p. 77. Why it is that TirrLwltM doubts the possibility of the passage of pus c^JLngm^ot^n^^^Jh lymph glands, is to me somewhat incomprehensible. cumabai, through § 226. It has been long supposed, and rightly so, from physiological experi- ences, that a lively interchange of matter takes place in the lymph nodes between the blood and the lymph. The same is taught us by the chan^ produced in the glands in question in morbid states of the juices of fh! ORGANS OF THE BODY. 419 body, manifested by inflammatory appearances and swellings of these organs. Thus Ave see that the lymphatic glands of man are liable to vary much in structural appearance, which must be partly attributable, no doubt, to the metamorphoses accompanying increasing age. Among the latter may be reckoned the partial transformation of the connective-tissue frameAvork into fat cells, and degeneration of the reticular connective substance into ordinary fibrous tissue, Avith consequent gradual obliteration of the whole organ. A third change observable in lymph nodes is true pigmentation. This affects principally the bronchial glands, and is almost invariably to be met Avith after a certain age, though with varying degrees of intensity. It may be due to the irritation of inflammation in the pectoral organs. Small granules of melanin (p. 52) are formed by the gradual metamor- phosis of the colouring matter of the blood. But though this may be accepted as one source of black pigmentary molecules, the latter have a very different origin, most probably, in many other cases. They are, namely, particles of carbon in a state of the most minute division, given off as soot from lamps, &c, and inspired and conveyed from the lungs into the lymphatic glands (Knauff). Eut between these two kinds of molecules we are at present unable to distinguish with any certainty. They lie utterly without order, partly within the lymph corpuscles, and in peculiar lumpy masses, and partly in the ground-Avork of the septa and walls of the vessels. In some instances the follicles appear to be the parts most affected, in others the lymph tubes of the medulla. A slight amount of this "melanosis" communicates to the bronchial glands a mottled appearance, Avhile strongly marked it may cause the whole organ to appear uniformly black. The effect on the lymphatic glands of inflammation of neighbouring parts is most evident. The meshes become narroAver in the framework ; the bodies of the ceUs of the same become plump, their nuclei undergo division, while great distension of the capillaries is also observed,—in fact, the whole gland acquires more or less the appearance it presented at an earlier age. Later on the reticular framework may grow luxuriantly, the distinction between medulla and cortex ceases to be apparent, the lymphatic system of canals disappears, and the whole organ becomes in- capable of functionating. The development of the lymphatic glands in the embryo, as Avell as their nature, was until quite recently entirely unknoAvn. That their origin, together with the whole vascular system, was from the middle germinal plate, is all that was knoAvn about them. This bad been demon- strated years ago by Remak. The labours of Sertoli and Orth, however, have recently throAvn some light upon the subject as regards these points. According to the interesting, but by no means exhaustive treatise of the first of these observers, there may be seen in the mesenteric glands of the ox, in the first place, a system of lymphatic canals at that spot where the connective-tissue nucleus or hilus-stroma of His is to he found. Around this system a quantity of connective-tissue, rich in lymph cor- puscles, is gradually developed, from Avhich the cortical substance, in the first place, takes its rise, and then the lymph tubes of the medulla. The investing spaces and cavernous passages of the medulla make their appearance subsequently, as Avell as the capsule, septa, and reticidated tissue connected with the latter. 420 MANUAL OF HISTOLOGY. As to the composition of the lymph glands but little is known. They contain a certain amount of leucin as a product of decomposition, according to Stddeler, and may also, it appears, contain uric acid, tyrosin (1), and xanthin (1) Krause and Fischer state the specific gravity of the organs in question to be 1*014 in the human being. §227. Nearly related to the organs we have just been considering, we find others which consist partly of single follicles, and partly of a number of the latter crowded together closely, and held thus by a peculiar connect- ing substance. These are mostly situated in the mucous membranes or submucous tissue. Among these may be reckoned, as occurring in the human being and mammalia, the so-called trachoma glands or lymphoid follicles of the conjunctiva, the lingual follicular glands, and tonsils, cer- tain irregularly occurring follicles of the gastric mucous membrane (lenti- Fig. 411.—Vertical section of a Peyerian gland Kie- 419 R0n«„io,. ■,,„.♦„ ^ :r TcSiertine o£ the mbui a< ^^^e^i^z villi, b, <,, follicles. vermiform appendix of the rab- bit, 1. Deeper portion in hori- zontal section, a, framework; b, lymph canals. 2. Superficial portion; a, b, as in 1; c, depres- sion in the mucous membrane lined with cylinder epithelium. cular glands), and the solitary and agminated glands of the intestine, or Peyers patches (fig. 411). ' That large massive organ, the thymus, may also be mentioned as pre- senting a similar structure. * This whole group including the lymphatic glands themselves, may be named with propriety the group of lymphoid organs. In addition to them we have, finally, the spleen, though no doubt a modified form In all those organs first mentioned, which belong to the mucous mem branes, we find the follicle as the essential structure. It cZlZn21 is structure to the analogous elements of the lymphatic glands and con sists of a reticular substance enclosing lymph corpuscles (comp t 400 and 412). Ihis presents not unfrequently in its interior a loose andopen- meshed appearance, whilst more superficially the network becomes der,C and further outAvards still, on the -urfcc^L^^l/cl^^tt^ ORGANS OF THE BODY. 421 JU have seen it in the lymph-nodes (§ 223). The vascularity of these mucous follicles is liable to vary to a considerable extent. In some of them, such as those ofthe conjunctiva, the capillaries only occur sparsely, in the form of very open interlacements; Avhile in other cases we ob- serve an extremely com- plex and delicate network, the tubes having, to a cer- tain extent, a radiating arrangement Avhen viewed in transverse section. Fig. 412, sketched from such a preparation of one of Peyer's patches from the rabbit, Avill serve as an example of the latter form. These rounded follicles, sometimes spherical and at others vertically elongated, are situated either in the tissue of the mucous mem- brane itself, or Avhen of considerable length, they project down into the sub- mucosa. Their upper por- tion [the cupola (fig. 414, d)~\ may be covered by a thin layer of mucous tissue [conjunctival follicle (fig. 415)], but may also advance so far for- Avards as to be covered merely by an epithelial coating lying directly on the reticulated sustentacular tissue [tonsd Peyer's follicles (fig. 413)]. In the middle equatorial region [" mesial or equatorial zone" (fig. 414, e)] the follicle is connected to a greater or less extent Avith the adjacent parts ; sometimes with the neighbouring mucous tissue, which in that case pre- sents, for a certain distance, the same reticular character, containing also lymph corpuscles, and at other points with abutting follicles. Thus we see, for instance, in the vermiform appendix of the rabbit—a portion of the intestine consisting entirely of crowded oval follicles—that the latter are regularly united in the neighbourhood of their equator by bands of lymphoid tissue (fig. 412), whilst the whole lower half ofthe follicle (the base) exhibits the same continuous investing space as in the lymph nodes. The analogy, hoAvever, is even more perfect than might be inferred at first sight, for careful observation teaches that here also a system of fibrous septa exists, Avhich, springing from the submucosa, passes under the follicles, and sends up partitions perpendicularly betAveen them. These spaces are even lined by the same characteristic endothelial cells, as those seen in the lymph nodes, according to His. Should these extensive investing spaces be absent, the follicles of each group are usually united to one another by means of reticular lymphoid tissue. The latter, in contradistinction to that of which the follicle itself is composed, exhibits a much closer texture, so that under the microscope it appears as a dense and non-transparent layer, Avithin which the more Fig. 413.—Transverse section through the equator of three Peyer's patches of the same animal, a, the capillary net- work; b, of the larger circular vessels. 422 MANUAL OF HISTOLOGY. loosely woven follicles are observed to lie. This condition of parts may be seen in the tonsils and conjunctival follicles. Fig. 414.—Vertical section of one of Peyer's patches from the human being, injected through the lymphatics, a, villi with their absorbent radicles; 6, glands of Lieberkuhn; c, muscular coat of the mucous membrane; d, cupola of follicle; e, mesial zone; /, base; gr. passage of the chyle-radicles of the villi into the true mucous membrane; h, reticulated arrangement of the absorbents about the mesial zone; i. course of the latter at the bases ofthe follicles; and *, their confluence to form the lymphatics ofthe submucosa; ', follicular tissue of the latter. When this arrangement prevails the investing spaces cannot be said to be entirely Avanting, they are rather converted into a system of narroAv passages, Avhich interlace upon the surface of the follicle " like the net upon the surface of a child's toy Indian rubber ball." The view that holds these passages around the follicle to be lymphatic canals is shown to be correct by injection (fig. 415). We observe that, from the surface of the mucous membrane, and mostly from the neigh- bourhood of the follicle generally, e.g., in many of Peyer's patches, from the adjacent villi (fig. 414, a); and in the case of the conjunctival follicles from the mucous mem- brane, especially on the surface of the band of union (fig. 415, c) ; that lymphatic vessels Avhich take the place of the vas afferens of the nodes are conducted to the surface of the follicle, either simply(fig.415),orwithacertain amount of complex interlacement (fig. 414, g). Arrived here, they open into either the investing space or its retiform equivalent (fig. 414,7,, i; 415, c). Those submucous lymphatic /. n vessels, Avhich take on such a variety of forms (fig. 414, k; 415, a), are the conduits correspond^ to the vasa efferentia of the lymph nodes; in short, the parallel between these Fig. 415.—Trachoma gland from the ox in vertical section and with injected lymphatic canals, a, sub- mucous lymphatic vessel; c. distiibution of the same to the passages of the follicle 6. ORGANS OF THE BODY. 423 latter and the follicles of the mucous membrane is almost complete. The latter may be regarded as small lymphatic glands occurring in mucous membranes, Avith Avhich view the simi- larity of the pathological changes occur- ring in them to those observed in lym- phatic glands, is in perfect accordance. / §228. The thymus gland, a double organ whose function is unknown, and which is, as far as Ave are at present aware, similar to a lymph node in structure, exists in full development only during the earlier periods of life, falling, later on, more and more a prey to fatty de- generation. Thus it is only exceptionally to be recognised in the bodies of older individuals. The first point Avhich we observe in the structure of the organ is that, besides being exquisitely lobulated, it possesses a very vascular fibrous envelope. Owing to the fact that the latter invests the internal mass but very loosely, the glan- dular tissue of each half of the organ may, after severance of the blood-vessels, be disentangled from it in the form of a band-like skein. The latter consists everyAvhere of a venous and arterial twig of accompanying lymphatic vessels, and a peculiar gland-duct, knoAvn as the central canal, upon which are situated, externally, the lobes and lobuli of the gland. When dissected out, the Avhole is of considerable length (fig. 416, 1). The central canal, which, accord- ing to His, has in the calf a diameter of only 0*7444 mm., is twisted up into a kind of spiral in the natural state, and the lobes are in close contact Avith one an- other. If Ave proceed with our analysis, Ave find that each lobe is made up of a num- ber of smaller lobuli, and the latter, enclosed within a vascular envelope of con- nective-tissue, are again composed of smaller polyhe- dral structures, flattened one against the other, whose diameter is 0*5640-1*1128 28 Fig. 416.—1. Upper portion of the thymus of a foetal pig of 2" in length, showing the bud-like lobuli and glandular ele- ments. 2. Cells of the thymus, mostly from man; a, free nuclei; b, small cells; c, larger; d, larger, with oil globules, from the ox; e,/, cells completely filled with fat at /, without a nucleus; g, h, concentric bodies; g, an encapsuled nu- cleated cell; h, a composite structure of a similar nature. Fie. 417.—Portion of the thymus of a calf (after His), showing the arterial, a, and venous rings, b; the capillary network. c; and the cavities ofthe acini, d. mm., or, in the calf, 1*1128-2*2256 mm. 424 MANUAL OF HISTOLOGY. These are the elements of the gland, the so-called granules or acini of the thymus. At first sight they remind us forcibly of lymphoid follicles. Under closer observation, hoAvever, important differences manifest them- selves. Externally, these acini of the thymus are separated from one another by deep indentations, whereas, internally, they become united, as many as fifty of them together, to form a medium-sized lobe—recall- ing to mind the state of things observed in the racemose glands. Then— and great stress must be laid upon this point—the thymus element appears hollow in its interior, and the cavities of the thick-Availed acini of each lobe unite, as in the racemose glands, to form its common passage. This then joins with similar canals belonging to other lobes, until, by a repeti- tion of the occurrence, the spiral central canal of each half of the organ is produced. Even in the walls of this common duct, bulgings or attached acini, or groups of the same, may be remarked, so that its thickness varies at different points. As to the texture of the acinus, we find that the central cavity, occu- pying about \-% of the whole diameter, is bounded by a layer of soft tissue. This consists of an exceedingly dense netAvork of stellate cells of reticular connectiA*e-tissue. The narrow meshes of this structure are occu- pied here, as in the lymphoid follicles, by an immense number of lymph corpuscles. A very delicate membrane, richly supplied Avith blood-vessels, coA^ers its surface. The blood-vessels, farther, Avhich traverse the follicular tissue, are also very numerous, and possess the Avell-knoAvn adventitia (§ 202). With the exception of a few stronger tAvigs, these are for the most part capillaries of 0*0063-0*0068 mm. in diameter. Injection of these brings out their arrangement in the most instructive manner. From the larger vessels of the central band smaller twigs are given off to the lobuli. Here they eventually form (in the calf) delicate circular and arched groups of arterial and venous branches (fig. 417, a, b) around the individual acini. Springing from these the capillaries are seen inter- nally (c) taking a convergent course, and forming a most exquisite net- work amid the lymphoid substance. Close to the central cavity they double on themselves (d) according to His. In the thymus of the infant, though the arrangement of the capil- laries is the same, an exception is so far to be seen to this arrangement of parts, that while the vein courses along at the periphery of the acinus as in the calf, the artery and its system of finer tubes occupies the interior of the glandular tissue near the central cavity in a manner wholly different. In the small meshes of the reticulum it has been asserted that numbers of free nuclei maybe seen (fig. 416, a) suspended in an acid, viscid, albuminous fluid. The essential element is, however, beyond doubt a small nucleated lymphoid cell (b) measuring 0*0074 mm. in diameter. More randy Ave meet with large cells of from 0*0046 to 0*0023 mm.', containing several nuclei, from 2 to 8. Ecker mentions further, as a phenomenon of retrograde development, that a deposit of fat globules takes place (d) in many cells, which, as soon as the organ is on the decline, run together to form one large drop, filling the Avhole body of the elements in question (e,f). He states, besides, that in older cells he has not unfrequently observed an absence of nuclei (/). But there are other structures to be met with here which are by no means connected with the involution of the thymus; these are the so- called concentric bodies. ORGANS OF THE BODY. 425 Around certain single cells, namely, Avhich appear not unfrequently to be undergoing fatty metamorphosis, or again, about a group of the latter, we notice the formation of dense concentric layers, which may be seen on closer examination to be composed of flat nucleated cells, like pavement epithelia (Ecker, Paulitzky), reminding us of the formations in epithelial cancer, so Avell known to pathologists. The smaller examples of these bodies (g) are formed of a group of cells, sometimes filled Avith granules, sometimes with fatty matter, and in some cases still possessing nuclei; which is surrounded by the thick laminated rind alluded to ; they may attain a diameter of 0*0169-0*0208 mm. The larger structures of this kind (/*), measuring 0*0593 mm., are formed by a repetition of the process enclosing several of these smaller corpuscles. As regards the lymphatics of the thymus, we are still comparatively ignorant. That the chief stems accompany the arteries and veins through the central band, has been already remarked above; but besides these there ate finer lymphatic vessels to be seen. These are found in the interstitial connective-tissue of the lobes, according to His, in the form of delicately walled tubes, only coursing round the latter. They are even stated by that observer to open into passages about 00226 mm. in breadth, filled Avith lymphoid cells, which spring from the centre of the acinus. Through these tubes a communication exists, according to His, betAveen the central cavity and the lymphatic vessels, by means of Avhich the cellular elements can pass into the latter. From the fact, however, that up to the present no one has succeeded, by puncture, in tilling lymphatic vessels around the acini of the thymus, (and my own numerous experiments also teach me that it cannot be done); and as the discoveries of more recent date, relating to lymphoid organs, do not seem favourable to the supposition of such an arrangement of parts as His describes, the matter would seem to call for closer investigation. The final distribution of nerves in this organ is still enveloped in obscurity. As to the composition of the thymus (Avhose specific gravity is stated at 1 *046 by Krause and Fischer), analyses have been made by Simon and Friedleben. The former of these obtained from the organ of a calf three months old, about 77 per cent, of Avater, circa 4 of an albuminous sub- stance, traces of fat and 2 per cent, of salts. The thymus of the calf is further stated by Gorup, Frerichs, Staedeler, and Scherer, to contain large quantities of leucin, also hypoxanthin and xanthin, volatile fatty acids, such as acetic and formic; also succinic and lactic acids. The mineral constituents consist principally of phosphates and chlorides of the alkalies, Avith a preponderance of phosphoric acid and soda. The proportion likeAvise ofthe magnesian exceeds that of the lime salts. Sulphuric acid is only present in small traces. The presence of salts of ammonia is a fact of some interest (Frerichs and Staedeler). On the whole, its composition has some resemblance to that of muscle. The development of the thymus Avas first explained by Simon, whose statements Avere subsequently corroborated by Ecker. In the mammal, as far as' has up to the present been ascertained, it appears first in the form of an elongated and closed sac lying in front of the carotids, Avhich is filled Avith cells and granular contents. By a bulging of the Avails of this, numerous rounded prominences are formed, in which Ave have the first indication of the future lobes. By a repetition of the process the capsule of the glands is eventually formed. A subee- 426 MANUAL OF HISTOLOGY. quent liquefaction of the central portion gives rise eventually to the formation of the central cavities. From fig. 416, 1, representing tho gland of a foetal pig two inches long, in course of development, we may obtain some idea of the process, and understand better the structure of the gland at the period of maturity. The retrograde development of the gland takes place with decrease of volume by the formation, as has been already remarked, of fat cells at the expense of the tissue, by Avhich we are reminded of a similar meta- morphosis in the lymph nodes (§ 226). That fatty degeneration of the gland cells also occurs, has been asserted, as Ave have already said, by Ecker. The time at which the retrograde process begins appears to vary; it lies betAveen the eighth and tAventy-fifth years. § 229. We have'still to consider in conclusion one other organ belonging to the lymphoid series, namely, the spleen. Owing to the great difficulties attendant on the study of this organ, it remained, until a comparatively recent date the subject of but brief and unsatisfactory research. But, lately, through the labours, especially, of Gray, Billroth, Schweigger-Seidel, but more than all of W. Muller, we have been made acquainted with the leading peculiarities of its structure. In the latter it resembles a lymph node, even more strongly than the thymus. In fact, the spleen may be regarded, as I myself expressed it many years ago, after careful consideration of the subject, as a lymph gland in Avhich the system of lymphatic passages is replaced by the blood- vessels ; it might be named, perhaps, Avith propriety a blood lymph gland. The organ presents, in accordance Avith this view beside, a fibrous enve- lope with a system of trabecular or septa, and a sheath-like formation of connective-tissue around the vessels, a soft glandular parenchyma. The latter is of two kinds; it presents itself, in the first place, in the form of lymphoid follicles, and in the next as a broAvnish red friable mass, knoAvn as the pulp of the spleen. The first of these correspond to the elements of the same name found in the lymph nodes; the latter is more or less a modified species of the medullary substance. Beneath the serous covering, which may be isolated from the organ in the ruminant body, the fibrous envelope or capsule of the spleen appears. In man, on the contrary, this tunic is closely adherent to the investing peritoneum. It is seen, under the microscope, to be made up of a dense interlacement of connective-tissue fibrillae, Avith a preponderance of fine elastic fibres, and contains also unstriped muscular elements. The latter are present in large numbers in many of the mammalia, as, for instance, in the sheep, dog, pig, horse, and hedgehog, especially in the deeper por- tions of the envelope. In other animals of this class they do not make their appearance in such quantities, as, for example, in the ox; while in man the contractile fibre cells are present in but small proportion. The capsule Avhich invests the Avhole spleen is folded in at the point of entry of the vessels and nerves,—the so-called hilus,—and is continued further inwards in the form of sheaths to the various vessels. It accom- panies the ramifications of the latter (more strongly developed and massive around the arteries than the veins) doAvn to their finest twios. It exhibits, hoAvever, considerable variety in the various species of animals a point to which Ave shall be obliged to refer again further on. Beside-* the sheaths of the vessels, and continuous with them, Ave meet ORGANS OF THE BODY. 427 with another prolongation of the fibrous envelope of the spleen directed inwards in the form of a system of septa. In the nature of the latter, as regards the spleen of the several mammalian animals, extraordinary variety has been observed. Just as was the case in the lymph nodes, it is but very slightly developed in the spleen of smaller mammals, as, for instance, in that of the mouse, the squirrel, the Guinea pig and rabbit, while in larger animals, as in horses, pigs, sheep, and oxen, it attains a high pitch of development. In man, and in the dog and cat, on the other hand, it is but moderately marked, reminding us of the lymph nodes again. The more numerous the trabecular in any spleen the harder is the organ found to be. From the whole internal surface of the fibrous envelope there spring a multitude of fibrous cords and bands, varying as to their distance from one another, and as to the angle at which they are given off. Their diameter is about 0*1128-0*1279, or even 2*2556 mm. These trabeculce of the spleen traverse the organ in all directions, uniting and again branch- ing in the most irregular manner. They form, when in a state of perfect development, a very complicated sustentacular tissue. On the other side they are connected with the sheaths of the vessels, or continuous with the latter, especially the veins (Tomsa). Within the innumerable irregular spaces,—formed by the intercom- munication of these trabecular,—the glandular tissue of the spleen is con- tained. When the system of septa is fully developed, therefore, the spleen of the larger animals acquires necessarily a complexity of structure, rendering the recognition of its nature of great difficulty. On this account the spleen of smaller animals is the most suitable object for investigation, as was also the case Avith the lymph nodes. In its more minute structure the tissue of the trabecular resembles that of the capsule. Here we find, again, a closely woven Avhitish connective- tissue, with nuclei and elastic fibres; in addition to these, also, longi- tudinally arranged muscular elements. The latter present themselves, either in all the septa, as in the case in the spleen of pigs, dogs, and cats (Koelliker, Gray), or, as is stated by many, only in the smaller trabecular. Thus it is in the ox and sheep (Koelliker, Ecker, Billroth). In man the number of muscle fibres is small. §230. Now, in the cavities aiready described in the preceding section, amid this system of trabecular, the glandular or lymphoid portion of the gland is contained. This consists, as Ave have already remarked, of a network of cords or bands, the pulp tubes analogous to, but not identical with, the lymph tubes of the medullary portion of the true lymphatic glands. In this, and connected with it, a number of lymphoid follicles are imbedded, discovered some centuries ago by Malpighi, and named in honour of him Malpighian corpuscles (Milzkorperchen, Milzblaschen). In many respects these are exceedingly like the follicles of lymphatic glands. They are not, however, grouped peripherally to form, as in the latter, a cortical portion, but occur scattered throughout the Avhole of the pulp. Their relation and connection to the arterial part of the vascular system is very peculiar, calling for a feAV moments' consideration. It is only rarely that, as among the ruminants, the splenic artery makes its entry into the spleen as one single trunk: it generally divides into several branches before doing so. Each of the latter then preserves in 423 * MANUAL OF HISTOLOGY. the interior of the organ its own individuality as regards its ramifications. Soon after there commences a most extensive division and subdivision of the vessels, until, finally, the latter, greatly diminished in size, form a series of terminal groups, which have been long compared to the hairs of a paint- brush. But a more appropriate comparison has been made be- tween these " Penicilli" and the branches of a willoAV tree divested of its leaves. Fig. 418 gives a tolerable represen- tation of the arrangement re- ferred to. Drawing such a branch out of the tissue of the spleen. Ave may recognise on it the follicles of which we have been speak- ing. They are of a whitish colour, and hang on the fine arterial twigs like grapes on their stalk. , They are either Fig. 418.-From the spleen of a pig. a, an arterial twig attached by their border to the invested with its sheath, showing its twigs, 6, and artery, or the latter traverse attached Malpighian corpuscles, c. ,..■''... „ ,. ,, their interior; or, finally, the angles of division of such a series of branches may be surrounded by numbers of them for a considerable distance. In form they are some- times spheroidal, sometimes more or less elongated. Such spleen corpuscles are to be found in all the mammalia, although presenting much variety. In the human organ, however, they are less distinct as a rule than elseAvhere; and in bodies which have suffered from protracted illnesses they were formerly supposed not to exist, Avhile in those in Avhich death had occurred suddenly they AArere said to be always recognisable, even Avithout the microscope; as also in youthful corpses (von Hessling). For this reason they Avere looked upon even years ago as integrant portions of the human spleen. If Ave follow up the disposal of the vessels commencing at the hilus, we soon remark that it is liable to vary greatly in different animals. The sheaths of these tubes also are no less subject to variation. Though very imperfectly developed in the Guinea pig, rabbit, squirrel, and mar- mot, they attain a high degree of development in other animals, as, for instance, in the dog and cat. There the arteries enter the spleen in several branches, each of the latter accompanied by a vein and one or two nerves. Both artery and vein while passing in receive a sheath, but not in the same way. Around the artery the latter is loose, and only runs for a short distance unchanged, undergoing rapidly a peculiar lymphoid transformation. The vein, on the contrary, is accompanied for a much greater distance by a tight investment, closely united to its walls. On the smaller venous twigs the latter resolves itself into a few bands of connective-tissue, which sink into the septa of the spleen. .Deviations from this general plan are to be seen in the ruminants and the pig. Iu man the arteries and veins arrive in the spleen, already divided into ORGANS OF THE BODY. 429 from four to six branches. Down to tAvigs cf about 0*2030 mm. they are contained in a common sheath, possessing a thickness of about 0*2256 ram. at its commencement. This investing formation then becomes gradually finer and finer, until reduced to a thickness of 0*1128 mm., enveloping in this state arteries having a diameter of 0*2256 mm., and veins of 0*4512 mm. The arterial twigs with their sheaths then separate by degrees from the accompanying veins, and ramify independently. But about the venous tube the simple sheath extends somewhat farther still, becoming even- tually split up into fibres, continuous with the trabecular of the organ (W Muller). These sheaths exhibit the same minute structure, farther, as the trabecular. At those points, hoAvever, at which the arterial separates from the venous twig, the structure of the tunic of the former changes its nature. Its fibrous tissue is transformed into reticular lymphoid connective sub- stance, together with which a decrease in its amount goes hand in hand. The advancing metamorphosis also, commencing externally, attacks even- tually the proper tunic of the artery. Progressing still, this trans- formation, this construction of " lymph sheaths " gradually leads to more or less circumscribed swellings of different shapes, and these finally to the Malpighian corpuscles of the spleen (fig. 419, a). In fact, the latter, with their varied configuration sometimes roundish, in other instances elongated more or less, and possessing a diameter of 0*2256- 0*7444, or on an average 0*3609 mm., take their origin from the infil- trated sheaths of the arteries, from which they can be by no means sharply defined. Arterial twigs of 0*1579 and 0*0993 mm. in diameter, down to those of only 0*0203, are usually seen to possess this metamorphosed sheath, and may all acquire a great increase of size by its formation. OAving, hoAvever, to the fact that the position of the artery is by no means always the same as regards this infiltrated sheath, fur- ther variety may be noticed. The former, namely, may pass either through the axis of these elongated masses or more laterally. In those parts, also, converted into follicles, Ave meet, at one time, Avith an eccentric course in the arterial twig, at another Avith a more central one. This position, further, has an effect on the texture of the various parts of the sheath. In the lower degrees of transformation we usually meet with an ordinary loosely Avoven connective- tissue Avith lymph cells in its interstices. The same is the case Avith the sheaths of the arterial twigs passing along the bordais Fig 419—Section of the spleen of a rabbit, a. Malpighurn corpuscle; b, sustentacular matter of the pulp, with the interspaces filled with venous blood. 430 MANUAL OF HISTOLOGY. of follicles. When, however, these take a course through a SAvollen point, or even excentrically, or through a Malpighian corpuscle, the trans- formation usuaUy goes farther, leading to the formation of a tissue nearly adied to lymphoid tissue. Whilst in the lower degree of lymphoid infiltration the sheath alone is affected, and not the proper adventitia, in the more advanced stages of the same the latter is drawn more and more within the circle of lymphoid metamorphosis. Turning now to the follicle, we find the sustentacular tissue framework denser and more resistent peripherally, while within it possesses wider meshes, and is more delicate. At times the internal is marked off from the more cortical portion by a circular line, as in the rabbit, Guinea pig, and marmot. This arrangement, however, calls for closer investigation. Here also, as in the lymph nodes, Ave may distinguish in some of the expanded nodal points distinct nuclei. The external demarcation of a Malpighian follicle is never produced by a homogeneous membrane enclosing it, but always by reticular connective-tissue, even at those points where by its denser texture its surface is sharply defined against the adjacent structures. In other cases the follicle is continuous, as to its delicate framework, with the surrounding tissue of the pulp, Avithout any sharp line of limitation existing between them. Entangled Avithin the meshes of all these different portions, there appear, beside free (?) nuclei (Muller), a host of ordinary lymph cells, pos- sessing as a rule but a single nucleus. Some of them, hoAvever, are multinuclear when very large. Beside these there occur, although in no great number, elements formed of colourless granular matter, or again containing molecules of a deep yellow or brown pigment. As regards the vessels of those portions which have become infiltrated, and converted into follicles, there are also capillaries to be considered, besides those arterial twigs already referred to. Yeins, on the other hand, are entirely absent. In parts but slightly infiltrated, is to be found a slightly developed long-meshed capillary network, Avhereas those portions greatly swelled exhibit, as a rule, a far more highly developed meshwork of capillaries derived from a special and rather variable arterial tAvig. This latter either springs from the artery of the follicle itself, or approaches the Malpighian corpuscle from without. The capillary net- work itself varies also; in the first place, in different follicles of the same organ, and in the second place, in different animals. It is some- times met with presenting a more or less regular radiating arrangement of its capillaries with arched anastomoses, the tubes having a diameter of 0*0029-0*0081 mm. But far more frequently the disposal of these minute vessels is irregular both as to anastomosis, division, and diameter. Observing the texture of the capillaries more closely, we recognise beside those presenting the ordinary appearance, with an adventitia, such as are seen, for instance, in reticular connective substance (§ 202), others whose walls are exceedingly delicate wanting the double contour, but which may on the other hand exhibit great richness in nuclei. In speak- ing of the pulp Ave shall refer again to this point, which is of great im- portance as regards the arrangements for the circulation in the spleen. In man the nature of the lymphoid infiltration, and the mode of for- mation of follicles, is similar to that just described, although the trans- formed arterial sheaths, and their local thickenings, may display con- siderable variety. We must not forget, hoAvever, that we are obliged to undertake our researches into the nature of the human spleen under ORGANS OF THE BODY. 431 much more unfavourable circumstances than when dealing with animals, namely, long after the death of the individual, and not unfrequently in cases where death has been produced by protracted illness. Neverthe- less, we may easily satisfy ourselves as to the infiltration of the arterial sheaths, the local thickenings giving rise to follicular masses, and the analogous arrangement of the finer blood-vessels. §231. On passing beyond the lymphoid infiltrated investments, and also the follicles, the arterial twigs continue their course for a certain distance ramifying in the manner already described, but without any intercom- munication among their branches. Finally, they are resolved into a multitude of straight capillaries Avhich anastomose only to a very small extent with one another. These are of rather fine calibre, and are not unfrequently very tortuous also. They pass on,—taken as a whole,—eventually into the finest vascular passages of the pulp. Among the various mammals, hoAvever, the minute structure of these capillaries differs considerably. In the pig, the dog, the cat, and the hedgehog, most of them are (according to Schweigger-Seidel, Muller) enveloped in elliptical swellings of the adventitia. These " capillary husks," as they have been named by Schweigger-Seidel, which are of great frequency among the capillaries of the spleens of birds (Muller) con- sist of a pale, soft, and very finely granular mass, in which numerous delicate nuclei are imbedded. Their dimensions in the dog, cat, and hedgehog, are 0*0451-00600 mm. in breadth, and 0*0902-0*1489 mm. in length. The capillaries, enclosed either singly or in greater number in these husks, present the same tAvo-fold constitution of their walls, ahead}' described in the foregoing section. Other capillaries of the same animals just mentioned do not, hoAvever, show these husks, and corre- spond thus Avith capillaries of man and the rest of the mammalia. The latter present for the most part a strong wall, as far as their transi- tion into the vascular passages of the pulp, while some of them are seen to be more delicate, more richly nucleated, or as though formed of single apparently distinct vascular cells. Great variety, hoAvever, is seen among the lymphoid adventitiar of such capillaries. They may appear to be made up of a delicate mass of con- nective substance, with round or elongated nuclei in the nodal points or interstices, but may also become thicker, obtaining a more or less fibril- lated coat of connective-tissue externally, with a more loosely reticular portion internal to it, in whose interstices lymphoid and fusiform cells are situated; thus reminding us of the "capillary husks" between which and these there are intermediate forms. In possession of these points regarding the structure of the capillaries, we may now at last turn to the consideration of the pulp. This is found to be a very soft red mass, occupying all the interstices of the organ between the partitions, vascular sheaths, follicles, and those other consti- tuents already described. Its coarser and more minute structure is only recognisable after artificial hardening. The pulp is made up of a network of irregularly formed cords and bands of a medium diameter of 0*0677-0*0226 mm. (fig. 420, 6), which bound a system of spaces and cavities varying again according to the species of animal, but in every case designed for the reception of the 432 MANUAL OF HISTOLOGY. Fig. 420. venous blood. The former or pulp tubes, like the lymph tubes of the lymphatic nodes, spring, in the first place, in great number, and with J r gradual transitions from the ^ surface of the follicles. Here, as in the rabbit, Guinea-pig, hedgehog, and marmot, they may be, for the most part, concentrically arranged, the interspaces bounded by them naturally corresponding in direction. A similar origin of the pulp cords from the lymphoid infiltrated arterial sheaths as Avell as from the adventitiar of the last rami- fications of the arteries, may also be recognised. Eventually they are inserted into the fibrous trabecular of the interior. The tissue of the pulp lubes or pulp cords is a modification of the reticular connective species, and is of very delicate texture (fig. 421). It presents everywhere a reticulum usually of extremely fine fibres, but also of some- what more expanded bands. In some of the nodal points nuclei appear to be imbedded, al- though, owing to the great delicacy of the tissue, doubt still- exists as to Avhether they are actually im- bedded, or only ad- herent externally. If we uoav follow up the connections of this netAvork toAvards the follicles or thickened points of the arteries, Ave recognise the fact that the reticulated tissue of the pulp is continuous with the coarser and tougher sustentacular matter of these parts ; inter- mediate forms exist- ing between the two kinds. If we noAv examine with special care the numerous venous passages, and the limitations of the pulp cords towards them, Ave soon convince ourselves here also of the reticular character of the tissue in question. If successful in obtaining a view of the floor of one of these venous passages, as at c, we will soon come to the conclu- sion—«nd to this Henle Avas the first to direct attention—that the tissue Fig 421.—From the pulp of the human spleen. The preparation has been brushed out (combination), a, pulp cords with delicate re- ticulated sustentacula substance; 6, transverse section of hollow venous c.inals; c. longitudinal section of the same; d, capillary in a pulp tube, dividing at e; f. epithelium of venous canals; g, side view of the same; and h, transverse section. ORGANS OF THE BODY. 433 of these pulp elements is composed of a netAvork of fine circular fibres anasto- mosing at acute angles, which constitutes the boundary of the blood stream. These venous passages are clothed with a peculiar species of vascular cells. The latter are, as regards form, fusiform elements (fig. 421,/ g h), and present in man round and projecting nuclei. They lie in the long axis of the venous path, crossing, consequently, at right angles the meshes of the cellular network. They are non-adherent to one another—a pecu- liarity of the utmost importance—and on this account may easily present clefts between them if the venous passage be subjected to a more than ordinary distending force. Here, then, the distinctly impervious walls of other venous canals do not exist. The vascular cells in question have long been known, from the fact of their extending back into the larger venous trunks, but they were only recognised a few years since in the venous pulp passages by Billroth. They are to be seen with great dis- tinctness in the human spleen. In the small meshes of the network of the pulp cords are entangled the same lymphoid cellular elements in pairs or singly, which we have°already mentioned when speaking of the follicles and metamorphosed sheaths of the vessels. Pigmentary cells, and even free aggregations of pigment granules, golden yellow, brownish, or black, occur with such frequency in many spleens, that even to the unaided eye the colour of the pulp presents great variety. In addition to these elements a certain number of coloured blood corpuscles are regularly met with, at one time unchanged, at another twisted, distorted, and altered. In preparations which have been carefully managed, moreover, the important fact may be noticed Avith comparative ease, namely, that these corpuscles are situated in the meshes of the tissue of the pulp perfectly free, that is, unenclosed by any capillary walls. On leaving the blood stream they undergo, in fact, changes of various kinds; they shrink, they become fissured, and are thus converted into those pigmentary molecules of different kinds already alluded to. But the most remarkable feature in this decay of the red elements, is the production of those cells of the spleen containing coloured corpuscles, knoAvn noAv for many years. These structures, Avhich Avere a puzzle to the observers of early times, and to which have been given consequently the most various signification, have been already considered at pp. 77, 78. Here, as in other organs, the Adtal contractility of the membraneless bodies of the lymphoid cells enables them to take up into their interior, not indeed the Avhole blood corpuscle, perhaps, but fragments of its substance. That the lymphoid cells of the spleen possess this power of contracting, I saAv myself very clearly some years ago in water salamanders and frogs. Later still the phenomenon was observed most extensively among mammals also, by Cohnheim, and in the embryos of the latter animals by Peremeschko. In conclusion, we would point out that, owing'to the Fig. 422.—Cells from the spleen of man, the ox, and horse. a-d, from man; a, free nu- clei; b, ordinary cell (lymphoid corpuscle); c, nucleated cell with a blood corpuscle (?) in the interior; d, with two such; e, the same from the ox with several; /, a cell from the latter animal with fat-like granules; g-h. from the horse ; g, a cell containing several fresh blood corpuscles and granules, as in the last figui e; h, cell with an agglomeration of granules; i, the same, free; *, a cell containing small colourless molecules. 434 MANUAL OF HISTOLOGY. incomplete nature of the walls of the venous passages, these cells, con- taining blood corpuscles in every stage of development, may make their way into the stream occupying these passages, and thus become elements of the splenic blood. Besides these. Funke and Koelliker mention, as farther elements of the splenic pulp in young and sucking animals, other small yellowish nucleated cells, Avhich they hold to be young blood corpuscles in process of develop- ment. Our own experience does not enable us to offer any remarks on this point. §232. We have still to consider the course of the blood-vessels and of the hjmphaties in the organ with which we are engaged, and to glance at the arrangement of its nerves. Commencing with the veins, Ave find them liable to vary greatly in different mammals. They are remarkable for their large calibre and great distensibility, even Avhen the distending force is but very small, a peculiarity which explains the rapid physiological and morbid congestions with which this organ is affected. Among the ruminants,—as, for instance, in the sheep and ox,—the vena lienalis enters the organ as a single trunk, parting* with its adventitia, and soon after its media, to the surrounding connective-tissue sheath, and then divides into wide branches, Avhich send off a number of lateral twigs, whose Avails consist above of a very thin membrane, so that these appear on section as interstices in the parenchyma of the spleen. In their further ramification, these vessels present an arborescent appearance, the branches springing from them at right and acute angles, and no anasto- mosis taking place among them. Thus the whole arrangement assumes a peculiar character, from the fact that these venous ramifications (whose calibre is remarkably great), breaking up rapidly into finer twigs, are directed towards the numerous Malpighian follicles in greater or less number. All these venous tubules are possessed of Avails of extreme tenuity, but Avhich are usually entire nevertheless. They consist, as a rule, of a layer of fusiform cells, 0*0029-0*0079 mm. in breadth, and 0*0201-0*0501 mm. in length, whose elongated nuclei project to a small extent above the surface of the cell. Externally the finer twigs are enveloped in the reticular tissue of the pulp already mentioned. Venous branches of this kind have been named by Billroth " capillary veins," or " cavernous splenic veins." They are met with in all the mammalia, though presenting much diversity as regards arrangement, by Avhich again the form of the pulp-cords is also modified. Whilst among the ruminants these cavernous veins pursue their course with acute angled division, and without anastomosis, they break up into branches among other animals, more or less, at right angles, in the primary dendroid ramifications, and communication amongst the twigs of the latter takes place, so that eventually, and by degrees, a regular network. of like-sized venous canals, or more or less expanded passages, is formed. This reticular arrangement is seen, for instance, in the spleen of the rabbit, the Guinea-pig, the marmot, and likewise in man. In certain cases the spleen of the infant displays with peculiar beauty this retiform intercommunication of venous canals, and in such instances the lateral twigs springing from ensheathed trunks assume almost immediately a net-like character. I myselt was the first to establish, in the year 1860, ORGANS OF THE BODY. 435 their venous nature by means of injections, and it was from my prepara- tions that Billroth became acquainted with them. Their diameter is on an average, 00169-00226 mm., Avith extremes of 0*0113 and 0*0282 mm., and their structure precisely the same as in the sheep. A spleen of this kind, on the Avhole, presents, in regard to its pulp, great similarity to the medullary mass and medullary passages of lymphatic glands. Here too, as in the sheep and all other mammals, the walls gradually assume a more and more interrupted character, ■ by separation of their vascular cells, and thinning down of their cribriform substratum, so that clefts leading into the hounding pulp-cords are formed. Finally, diminished to 0*0158-0*0099, all the cavernous veins conduct the blood everywhere into the venous radicles with their fissured Avails and defective vascular cell-lining. §233. Having noAv folloAved the cavernous venous passages doAvn to their finest subdivisions, the lacunar venous radicles, bounded only by the tissue of the pulp, we next come to the important question so much dis- cussed Avithin the last few years, namely, How does the blood from the ultimate ramifications of the arterial system find its way into the radicles of the venous ? Many observers, among whom Gray, Billroth, and Koelliker may be mentioned, believe that fine terminal capillaries open immediately into . the cavernous veins without having formed previously any true network. Schweigger-Seidel supposes the transition to take place through peculiar vessels formed of fusiform cells alone. The Auews, however, of Key and Stieda are quite different. According to them, there exists betAveen the capillary ramifications of the arterial system and the cavernous veins an extremely dense network of most delicate capillary vessels with distinct walls, in whose tiny meshes the lymphoid cells are entangled, and which, in broad terms, constitute the pulp. Many of these views are based upon the appearances produced by incomplete injection or improper interpretation of preparations good enough in themselves. Thus it not unfrequently happens that we believe we see direct open- ings of capillaries into veins, which prove, on closer inspection, to be in almost all cases optical illusions. We do not wish, however, to characterise these immediate transitions as impossible. We have, indeed, ourselves, during a long study of the subject, met Avith appearances hardly capable of any other interpretation ; but their number Avas extremely small, so that the conclusion that they Avere only exceptional Avas forced upon us. Our own studies, therefore, compel us to dissent from the opinion of G'ray, Billroth, and Koelliker on this point. Key and Stieda, on the contrary, have determined the true mode of transition, but have mistaken an extremely dense reticulum of very delicate lacunar passages for a network of capillaries possessed of distinct Avails. The fact is, that the passage of the arterial blood of the spleen into the veins of the latter takes place in man and the mammalia generally in small streams, having no special bounding walls. The blood traverses the network of the pulp and interstices of the lymphoid cells contained in the latter in the same manner—if we may be alloAved the comparison-- as the water of a SAvelling river finds its Avay through the pebbles of its 436 MANUAL OF HISTOLOGY. bed. These interstices have been named the intermediate pulp-pas- sages. We have to thank W. Muller for being the first to place the existence of these lacunar beyond doubt, although such an arrangement of parts had been already pointed out here and there. Our own observations on the spleens of the sheep, rabbit, Guinea-pig, mouse, mole, and human being, have led us to the same conclusions on the subject as those arrived at by the gentleman just mentioned. # To understand correctly, however, the nature of these pulp-passages, it will be necessary to return for a moment to those ultimate ramifications of the arteria lienalis already dealt with in section 230. There we con- sidered fully the capillaries of the simply infiltrated arterial sheaths of the lymphoid swellings on the latter and of the Malpighian corpuscles. In all these parts, either the usual structure of the capillary tube was presented to us, or a modified and much thinner wall indicative of its approaching transformation. But all these capillaries to which we referred make their Avay into the pulp of the spleen, becoming merged, after a shorter or longer course, in the Avail-less passages of the tissue, either single or branching. We not unfrequently meet Avith spleens Avhose pulp must be said to be rich in long capillaries, Avhich occupy the axes of the pulp-cords in a Avay reminding us of the lymph tubes. As to the mode noAv in which these capillaries run out, the folloAving points may be recognised (fig. 423). The Avails of the little vessels become, as they are about to run out, finer and thinner Avithout exception, besides Avhich they appear delicately granular, as well as richly studded, with nuclei imbedded in their substance. Subsequently we notice a regular fibrillation commencing in the tissue of the wall, the' nuclei, with the portion of tissue adjacent, developing into separate bands and fibres, pale in colour, Avhich are inserted continuously into the reticulum of the pulp. We are often uncertain, indeed, for some distance, Avhether avc have still before us the passage of a capillary on the eve of termination^ or a canal-like interstice of the pulp. Naturally, at these points, the matters injected into the capillaries find their way into the adjacent por- tions of the pulp. " ORGANS OF THE BODY. 437 Noav, the latter, as the reader is already aAvare, is formed of a very narroAv-meshed retiform sustentacular substance, whose interstices are occupied by lymphoid cells. Between these latter, and along the fine bands of the reticulum, we find that the injection (a) passes further into the pulp. If glue have been employed, the mass hardens subsequently in the form of thin but irregularly defined shell-like fragments around the lymp corpuscles of the pulp, broader at one spot than another. The diameter of each stream varies from about 0*0032 to 0*0090 mm., and is of course affected by the amount of force exercised in injection. The great distensibility of the spleen observed during both health and disease, and which is sufficiently known to every one who has devoted any time to its artificial injection, is in a great measure owing to this capacity for dilatation of the intermediate pulp-passages. It Avas the contemplation of such appearances under the microscope Avhich led to the view supported by many recent observers, that there exists in the pulp an intermediate network of very delicate capillaries, bounded by special Avails. At the same time, the reticulum of the pulp was erroneously held to be formed of the collapsed canals of this net. It is quite obvious that a slowly increasing pressure will fill a larger and larger portion of this system of interstices in the pulp. Thus we see the Malpighian corpuscles encircled by rings of the reticulated passages ; and eventually the matter employed for injection may advance into the more superficial portions of the same, and give rise there to the same appearance of retiform interlacement. But, finally, the injection (b) advances from the pulp (fig. 424, a) into the radicals of the veins (c) already known to us from the preceding section. To its progress there are no obstacles, from the fact that the radicles of the veins are nothing else than interstices found in the tissue of the pulp ; and, therefore, enclosed by the same reticulated tissue Avhich had been filled through the capillaries. If, for the control of these artificial injections, other natur- ,.,.,, «„„w„5„-^ ,. .... , J n ' i „nf„U„ Fig. 424.—From the spleen of the sheep (doublemjec- ally filled Spleens be CaretUlly £ion) a< sustentacular network of the pulp; b, in- PYflminpd in Avhich the red blood- termediate pulp-passages; c, their transition into examined,m Avnicn me ieu uiuuu ^ ^^ ^.^ witn their imperiect i,m,tation; cells have been preserved by a, venous twig. certain modes of treatment, and the Avhole hardened, Ave will observe that at the terminal portions ot the capillaries these coloured elements are prolonged in wall-less pas- sages between the lymph corpuscles, and at other points arranged together in similar rows and groups, which coalesce to form the wail-less radicles of the veins. . . . Thus seeing that both artificial and natural injection point to the same conclusions, we may venture to sum up as follows: the blood from the arterial capillaries is emptied into a system of intermediate passages, which are directly bounded by the cells and fibres of the network of the pulp, and from which the smallest venous radicles with their cribriform Avails take origin. 438 MANUAL OF HISTOLOGY. §234. As regards the lymphatics of the spleen, it was for some time believed, from the results of injection, that it only possessed such vessels on its surface. These are situated underneath the serosa, and are arranged in a very complex network, in the ox, sheep, and pig, formed of valved vessels of considerable size (Teichmann, Billroth, Frey). In the first animals mentioned these vessels may be easily injected, and are seen then to present a number of bead like dilatations at various points. From the fact that during injection of the external vessels the matters employed for that purpose could not be forced into any deeper lymph passages in the parenchyma of the spleen, and that it had been already ascertained that the Malpighian corpuscle is not possessed of anything corresponding to the investing space of the lymph follicle, the spleen came to be regarded as an organ analogous to the lymph nodes, but in Avhich the internal lymphatic passages are replaced by venous canals. The well- knoAvn participation of the organ in the life of the blood, the entrance of lymphatic cells into the venous stream, and the very probable destruction of multitudes of red corpuscles within the organ, all seem to justify its being declared a blood lymph gland (Frey). Of course, the denial just mentioned of the existence of internal lymphatics led to contradictions of the older views, based upon the stated entrance of absorbent tubes at the hilus of the organ, together with the arteries and veins (Ecker, Koelliker, and others). While the super- ficial lymphatics, namely, were found to contain a pellucid fluid, those of the interior were stated to be filled with a coloured liquid reddened by the presence of blood-ceUs. A few years ago, however, Thomsa demonstrated lymphatic vessels in the horse's spleen, and moreover in communication with those of the surface of the organ. They traverse partly the banded sustentacular matter, folloAving the ramifications of the veins, and partly the connec- tive-tissue of the sheaths of the vessels, together with the stronger arterial tAvigs, whose finer ramifications they completely ensheath eventually. Now, the statements of this talented observer have not the slightest trace of inconsistency about them. Here, as elsewhere, we find muscular and connective-tissue structures traversed by lymphatic passages, and, owing to the lymphoid transformation which comes over these sheaths continuous on the other hand with ordinary connective-tissue, the lymph cells may be supplied to the fluid from such localities. But when Thomsa states, further, that the final ramifications of the internal absorbents conduct eventually into the follicles and pulp, and there clothe the individual lymph corpuscles and agglomerations of blood- cells with ring-like passages, Ave cannot rid ourselves of the greatest doubt upon the point, nor avoid regarding what he has observed as probably the result of extravasation into a tissue we know to be so fragile. We' can hardly conceive it possible, that beside the almost ubiquitous blood stream, unconfined by a definite wall, a similar lymph stream could have room to exist, and such an extensive peripheral mixture of lymph and blood would be without any analogy in all that has as yet been observed in the body in the two systems. But whichever view is correct, the significance of the spleen as a blood lymph gland is by no means shaken. The nerves of the spleen having their origin from the plexus lienalis of ORGANS OF THE BODY. 439 the sympathetic, consist principally, and not unfrequently almost exclu- sively of pale elements already known under the name of Remak's fibres. They enter at the hdus, and pursue the same course as the ramifications of the arteries. The number of nerves supplying the organ is very con- siderable as a rule, but their mode of termination, judging from Koel- liker and Billroth's observations in the sheep and ox, is still uncertain. Division of their trunks was observed by Koelliker, and Ecker probably saw terminal resolution. According to W. Muller, finally, there occur at certain points of the splenic nerves groups of cells like ganglion cor- puscles : once only did he succeed in tracing a fibre into a capillary sheath in the spleen of a pig. We are tempted to ascribe to the struc- tures in question a similar significance as the end capsules of Krause on the gland nerves (p. 327). §235. The spleen, Avhose sp. gr. is 1*058 (Krause and Fischer), contains 18- 30 per cent, of organic matter, and an average of 0*5-1 per cent, of mineral constituents (Oidtmann). That organic fluid of acid reaction, Avhich saturates the tissue of the spleen, contains, according to Scherer, Frerichs, Staedeler, Cloetta, and Gorup, a large number of interesting substances. Among these may be named inosite, volatile fatty acids,—e.g., formic, acetic, and butyric, also succinic, lactic, and uric acids. Among the bases we find, in the normal human spleen, considerable quantities of leucin, and a moderate, that is comparatively large amount of tyrosin (Frerichs&nd.Staedeler). Xanthin and hypoxanthin are also encountered in the organ. Beside these, Scherer succeeded in obtaining non-carbonaceous pigments, a very interesting albuminous substance rich in iron, and much iron combined, it appears, with acetic and lactic acids. The peculiar con- stitution of the veins must provide for the passage of these matters into Lhe circulation, but up to the present no analysis of the blood of the splenic vein has come upon them there (comp. p. 121). Special attention has been bestowed by Oidtmann upon the mineral con- stituents, and among them he has found chlorine, phosphoric, sulphuric, and silicic acids, potash and soda (the latter preponderating), lime, magnesia, iron, manganese, and copper. Turning, then, to the physiological significance of the spleen, so fre- quently a subject of debate, it is supposed to play an important part in the economy of the blood. It is believed to be concerned, namely, in the destruction of the blood-cells on the one hand ; on the other, in the repro- duction of the same. The first of these views may be defended, but not incontrovertibly proved in the present state of science; for although, m many spleens, the blood-cells are certainly very extensively destroyed, still a doubt exists whether this is anything more than an accidental occurrence. The second theory appears, however, more capable of proof. According to it the spleen may be regarded as analogous in function to the lymphatic nodes, producing the colourless cells of the pulp, which on finding their way into the blood, are known there as white blood corpuscles, and which possibly, in part at least, undergo ere they leave the cavernous portions of the tissue of the spleen a transformation into coloured cells. The amount of blood in the organ, further, is influenced m various ways by its fibrous and muscular elements. The elasticity of the former opposes to every expansion an amount of resistance varying with the volume ot 29 440 MANUAL OF HISTOLOGY. the contained blood, while the periodical activity of the muscular elements presided over by their nervous systems leads to the expulsion of the fluid contents of the spleen towards the point of least resistance, namely. the veins and lymphatic vessels, and so to a decrease of volume in the organ. In support of the theory that the spleen is a species of accessory or modified lymphatic gland, providing for the reproduction of colourless blood-cells, we have, in the first place, the parallelism which exists in the changes taking place in both these organs in certain diseases, then the greater richness of the blood of the splenic vein in white elements (§ 70), and, finally, the analogous structure of the spleen and lymph nodes. This latter point, namely, that of similarity of structure between the spleen and lymphatic glands, is most easily demonstrable in the lizard and snake, in which a definitely enclosed stream of blood is seen to flow betAveen certain follicular masses (W. Muller). Gray's view is that the spleen serves the purpose of a reservoir for a certain quantity of the blood. Schiff, on the other hand, regards the organ as an auxiliary to the digestive apparatus, yielding to the pancreas its power of digesting albuminous matters. The origin of the spleen, as far as at present known, is from a special aggregation of cells belonging to the middle germinal plate, and quite unconnected with the digestive organs. These cells are subsequently metamorphosed into the various tissues of which the organ is composed. The first rudiments are remarked at the end of the second month. Accord- ing to Remak, the appearance of the Malpighian corpuscles is very early, but Koelliker believes, on the contrary, that it is only towards the end of intra-uterine life that they are formed. Other conclusions, however, on these points have recently been arrived at by Peremeschko. According to him the spleen is developed as an off- shoot of the pancreas. The envelope and trabecular, as well as the fine reticulated tissue of the pulp, is first formed; then the lymphoid cells, with numerous red blood corpuscles, make their appearance, at first in but small number; then, from the rapid increase in number of the lym- phoid elements, numerous collections of the latter are formed in the sheaths of the arteries, giving rise, at a very early embryonic period, to the Malpighian corpuscles. The numerous morbid changes in structure taking place in this organ require more careful attention than has up to the present been accorded to them, owing to insufficient acquaintance with the minute structure of the part Among these a great increase of volume in the organ, asso- ciated with an excess of white corpuscles or leucaemia, has awakened much interest. § 236. Pending a more satisfactory classification, impossible in the present state of histology, we shall for the present associate with the lymphoid parts a series of other organs whose functions are still a problem, and as to whose structure much doubt still exists on many points. These are the thyroid gland, the supra-renal body, and the pituitary body For the present we may retain for them the old name of blood-vascular glands In many cases they have already reached or passed their full development as met with in the adult body, and are engaged in retrogression or pro- cesses of decay,t r ORGANS OF THE BODY. 441 The thyroid gland is found to be made up of closed vesicles of roundish form embedded in vascular connective-tissue (fig. 425, a, b). These appear, at first sight, like closely grouped granules of 0*5641-1*1279 mm. in diameter, rounded or flat, and of a reddish-yellow colour. They are Fig. 425.—Two lobules from the thyroid of an infant. a, small glandular vesicles and their cells; b, the same with incipient colloid metamorphosis more strongly marked at c; d, coarse lymph canals; and e, fine radicals of the same; /, an efferent vessel of considerable size. again arranged in small lobules, and these in larger lobes, the considera- tion of which we leave for descriptive anatomy. The stroma is made up of ordinary fibrillated connective-tissue of toler- ably loose texture, mixed with elastic elements. The gland vesicles, 0*0501-0*1026 mm. in diameter, possess a limiting membrane formed of rather delicate homogeneous connective-tissue, Avhich is enveloped exter- nally in a dense round netAvork of capillaries. The latter of a diameter of about 0*0072-0*0115 mm. in the dog, and 0*0088-0*0115 and 0*0114 mm. in the calf, are arranged in meshes of an average breadth of 0*0201-0*0226 mm. Their internal surface (fig. 426, a, b) is clothed with low cylin- drical cells about 00196 mm. in height and 0*0113 mm. in breadth. These resemble epithelium, and contain nuclei of about 0*0086 in diameter (Peremeschko). The cells separate very easily from the walls in conse- quence of decomposition, and on their solution the nuclei become free. In the embryo the cavity of the round gland capsule is represented at first by a finely granular substance, in Avhich cells and nuclei are embedded. Later on the growing cavity is usually seen to contain a homogeneous, transparent, and almost fluid substance, knoAvn as colloid matter (p. 21). By it the whole interior of the gland capsule is com- pletely filled in the fully developed animal. The recent researches of Frey and Peremeschko have made us acquainted with the lymphatic vessels of the part. The whole envelope of the organ is covered by knotted trunks, Avhich take their origin from a network of very complicated canals, situated in a deeper layer of the former. This latter network is formed around the secondary lobules of the gland by the reticular intercommunications of these canals (fig. 425./). Fig. 426.—Colloid metamorphosis. a, glandular vesicle from the rabbit; 6, incipient colloid me- tamorphosis from the calf. 442 MANUAL OF HISTOLOGY. From the peripheral network formed of canals burroAving through the connective-tissue of the capsule, lateral ramifications are given off, which penetrate into the interior, and gradually enclose the primary lobes in complete rings, or more or less perfect arches (d, d). From these a feAV fine terminal passages Avith blind ends (e) are seen sinking in between the different vesicles. The nerves supplying this organ do not spring from the vagus or hypo- glossus, but from the sympathetic, entering with the vessels of the part. They consist for the most part of non-medullated fibres, forming trunks Avith numerous branches, Avhich ramify amid the connective-tissue between the lobes and lobules. Among them may be seen ganglion cells, partly isolated, and partly arranged in groups of from 2 to 5. Their mode of termination is as yet unknoAvn, except so far that fine terminal filaments are lost in the connective-tissue bounding the vesicles. Con- trary to the general opinion, the thyroid gland cannot be said to be poor in nerves, nay, in the calf it appears even to be richly supplied Avith the latter (Peremeschko). The structure, as it has just been described, undergoes, hoAvever, a rapid change, even at an early period, so that in the infant, even, we may meet over a considerable area with modified glandular tissue, in such quanti- ties sometimes as to render the recognition of its original structure of some difficulty. The glandular cavities now become more and more filled with a homogeneous transparent and semifluid substance (fig. 425, b, c), a product of the transformation of the gland cells to which the name colloid matter has been given (fig. 426). Later on in life the cavities just described undergo in the human being a great increase in volume through increase of the colloid matters, and most unmistakably at the expense of the interstitial connective-tissue, which suffers compression. An extreme degree of codoid accumulation leads not unfrequently in man to a considerable enlargement of the whole organ, constituting that con- dition known as goitre, the glandular struma of Ecker. This progressive colloid metamorphosis, in Avhich small whitish semi- transparent points may be seen even Avith the naked eye, gives rise to compression of the interstitial connective-tissue, and Avith it of the lymphatic canals embedded in it. In consequence of this the absorbent apparatus decreases more and more in efficiency, while the blood-vessels, Avhich remain pervious for a longer time, continue to supply material for a continuation of the colloid metamorphosis. Further accumulation of this substance leads to obliteration of the gland vesicles, the connective- tissue disappearing, and the cavities opening into one another. If we now examine a portion of the gland in which the process has advanced to this stage, each lobe appears as a pale yellow coloured jelly-like mass enveloped in a network formed of the dwindling and half-macerated con- nective-tissue bundles. Finally, it may come to pass that a whole lobe is metamorphosed into a pellet of colloid matter. Hand and hand Avith these changes anatomical transformations take place in the gland cells the latter becoming filled Avith the same substance, and finally undergo solution. The views regarding the functions of the thyroid gland are still only hypothetical. The fluid which may be pressed out of its substance con- tains leucin, hypoxanthin, as Avell as volatile fatty acid, and lactic and succinic acids. The specific gravity of the organ has been set down by Krause and Fischer at 1*045. ORGANS OF THE BODY. 443 From Remak's investigations as to its origin, it would appear that the thyroid springs in the form of a saccule from the middle line of the anterior Avail of the pharynx, and is formed consequently in the same manner primarily as the glands of the intestine. Soon after, however, it becomes completely separated from the pharynx, and out of the single vesicle two sacs are formed by division, Avhich assume a lobulated appearance from indentations and constrictions which are eventually developed on them. In the thickened walls of these sacs solid aggregations of cells are subse- quently formed, which are developed later on into the gland vesicles of the organ, becoming invested with an envelope of connective-tissue, within which a certain amount of fluid collects among the elements. The large main vesicle on each side appears, likewise, to give origin to glandular elements, by undergoing constriction at various points, and seems thus to work its own obliteration. According to Peremeschko, we not unfre- quently encounter division ofthe gland capsules as phenomena of groAvth. The thyroid gland is probably at its greatest pitch of development in the new-born infant, and becomes very sluggish in growth a few Aveeks after birth. § 237. The suprarenal bodies (glandulai suprareuales) have, on the other hand, a different origin from the last, namely, from the middle germinal plate. These are double organs, in regard to whose functions we are totally in the dark. Enclosed in a capsule they present considerable variety of sub- stance, both from an anatomical and physiological point of view, and we may distinguish a cortical and medullary portion. The cortical sub- stance is marked Avith radiating streaks in different animals, varying in colour from a brown or reddish, down to a Avhitish yellow, and is of a tolerably firm consistence. Contrasted with this the lighter greyish red or whitish medullary portion is less resistent. In man a dark narrow boundary zone may be observed betAveen these two portions, usually yellowish brown, but at times greenish or blackish brown. After death this breaks down rapidly, and becoming fluid, causes the loosening of the medullary part of the organ from the rest. The envelope (fig. 427, c) consists of connective-tissue with elastic elements. Externally it merges into formless areolar tissue, containing fat cells. Internally it gives off those numerous fibrous processes which traverse the organ, and in their ultimate arrangement form a frameAvork within which the cells are enclosed. Let us noAv glance at the cortical substance of the suprarenal bodies. Those band-like processes just mentioned are tolerably strong, and take a slightly convergent course inwards, giving to the cortex, which in man is about 0*6767-0*1279 in thickness, a fibrous appearance, distinctly visible even to the unaided eye. From these numerous bundles of connective-tissue coming off, laterally intercommunicate with others also given off from the internal surface of the envelope, giving rise to a large number of glandular cavities. Near the surface of the organ these latter are generally short, but soon attain considerable length as they follow the course of the septa, assuming a columnar figure (fig. 427, a, b; 428, a). In transverse section, however, these toavs of cells do not always appear round, but not unfrequently present to our view oblong, reniform, and crescentic configurations. Again, in profile, we may easily make out that euch gland cylinders divide and give off branches at acute angles. 444 MANUAL OF HISTOLOGY. Fig. 427.—Cortical portion of the human suprarenal body in ver- tical section, a, smaU, and 6, larger gland cylinders; c, cap- sule. Further inwards still the cavities of the cortical portion become shorter and shorter, assuming, consequently, a more rounded form. From this point on there commences, in the strong and but slightly altered septa of connective-tissue, a rapid fibrillation, the fibres converging so that the further Ave advance towards the centre of the organ, the smaller do the interstices become. •In the nodal points of this network we find nuclei, the general arrangement of parts re- sembling in many respects what Ave have already met with in lymphoid reticular con- nective substance (Joesten). The interstices in the cortex just alluded to contain a dark viscid mass, which is found, on closer inspection, to be made up of naked cells containing albuminous granules, and, not unfrequently, numerous fatty molecules also (fig. 428, a; 429, d). Within the soft bodies of°the former, Avhose diameter is about 00135 or 0*0174 mm., large nuclei may be observed, measuring from 0*0090 to 0*0056 mm. The . cells situated within the dark boundary zone already alluded to, contain large quantities of brown pigmentary granules. While the more internal and smaller meshes enclose but a few cells, the elongated and radiating compartments contain multitudes of them (fig. 428). The latter cavities are, besides, traversed by minute fibrous bands, forming a reticulum. As to a membrana propria, each agglomera- tion of cells was formerly supposed to be en- veloped in one, in the same manner as a glandular crypt (Ecker); but this covering certainly does not exist in our opinion. Elucidation of the structure of the delicate medullary substance is attended with great difficulties. We see, however, that at the inner border of the cortical portion the fine fibres of the frame- work, though very closely arranged, approach each other still more, and are inserted eventually into processes of a mass of tough connective- tissue, which occupies the centre of the organ en- veloping the stronger blood-vessels, and especially the large veins. Enclosed within this fine sustentacular sub- stance of the medullary portion of the organ, a number of large oval cavities are to be seen. These exceed in size those of the cortex, but do not possess the same radiating arrangement; they lie rather with their broad surfaces towards the centre and surface of the organ. In man these medullary cavities appear to be generally smaller and rounder than in other animals. - o Fig. 4'>8.—Cortical portion of human suprarenal body un- der high magnifying power. a, gland cylinders; 6, inter- stitial connective-tissue. ORGANS OF THE BODY. 445 Fig. 429.—Transverse section through the cortical substance of the human supra- renal body, a, framework of connec- tive-tissue; 6, capillaries; c, nuclei; d, gland cells. These interstices are likeAvise occupied by naked cells, with beautiful vesicular nuclei and finely granular bodies. Fatty molecules are present, however, in this case in but small quantity. The dimensions of the cells (0*0180-0*0350 mm.) exceed those of the cortical elements. Owing to their softness, also, they accom- modate themselves one to another. From the fact of their form being somewhat that of a thick angular plate, they recall to mind, when seen from the side, the appearance of columnar epithelium. It is a point worthy of note that, Avhile the cells of the cortical portions of the organ are but slightly affected by the action of bichromate of potash, the bodies of these which are now under consideration ac- quire a deep tinge of brown from immer- sion in a solution of this salt (Henle). The blood-vessels of the suprarenal body offer many peculiarities for our consideration. They are very abundant in this organ. Multitudes of small arterial tAvigs, partly from the aorta and partly from the phrenic, carliac, lumbar, .and renal trunks, penetrate into the interior of the suprarenal body with numerous ramifications, and break up there into a network of capillaries, Avhose elongated meshes are arranged in the direction of the radiating bands of tissue within the organ. These small tubes have a diameter of about 0*0059- 0*0074 mm., and folloAv the course of the connective-tissue processes which traverse the cortical substance. The meshes formed by them, measuring about 0*0451-0*0564 mm. in length, and 0*0293-0*0201 mm. in breadth, invest eventually the many agglomerations of cells already- alluded to. The medullary portion appears to have no true capdlaries, and the cortex is certainly destitute of venous twigs. On entering the medulla the arterial capillaries become larger, and form, by anastomosis, a number of vessels of considerable calibre. These, then, continue to join one Avith another at acute angles, maintaining,.as a rule, the direction of the capillaries of the cortex. Thus the whole of the medulla becomes occupied, to a great extent, by an uncommonly highly developed venous netAvork of tubes, measuring 0*0200-0*0293 mm. and upwards, with interspaces betAveen them of 0*0200-0*0345 mm. The union of these vessels produces larger, which empty themselves into the usually single large venous trunk, situated in the centre of the organ. Thus we find the cortical portion traversed by a delicate arterial interlace- ment, and the medulla occupied by a coarse venous network. As regards the lymphatics of the organ, we possess at present no reliable information. The chief interest, however, which attaches to the medulla is owing to its great richness in nerves (Bergmann) which are arranged here in many mammals in a highly intricate plexus of microscopic minuteness, in which, according to Holm, ganglion cells may he recognised. Owing to this it has been surmised that the suprarenal body has some connection with the nervous system. The final termination of the nerves is still unknown. The cortical portion often appears to be utterly devoid of nerve fibres. 440 MANUAL OF HISTOLOGY. As regards the composition of the suprarenal body, we only possess a few notes at present. Its specific gravity is, according to Krause and Fischer, 1*054. It contains leucin and myelin in large quantities (Virchow). Holm has also met with inosite and taurin in the ox. Among the graminivora, hippuric and taurocholic acids are also stated by Cloez and Vulpian to be present in the organ in question (?) Another matter was also discovered in the medulla by Vulpian, and its presence confirmed by Virchow, Avhich became red on exposure to the air and on the addition of iodine in solution, and blackish blue under the action of chloride of iron. We are stiU entirely in the dark as to the physiological significance of the suprarenal bodies. They are, hoAvever, liable to undergo many morbid changes, which have recently become the subject- of much con- sideration in their relation to the so-called Morbus Addisonii. This manifests itself in very emaciated subjects as a very deep discoloration of the skin, together with disorganisation of the suprarenal bodies. The tingeing of the skin is produced by the presence in the deeper layers of cells of the rete mucosum of either a diffuse or very finely molecular pigment of a yellowish or yellowish brown colour. That peculiar colouring matter in the boundary zone between the medullary and cortical portion of the organ Avhich Ave have already considered above, is very possibly con- nected Avith this very obscure and enigmatical phenomenon. The suprarenal body is developed at the same time as the kidney, but independent of it, from an aggregation of cells in the middle germinal plate. It is a curious fact, that during the earlier portion of intra-uterine existence these bodies at first exceed in magnitude the urine-secreting organs. At about the twelfth Aveek in the human subject they are about equal the latter in size, and from that on they remain more or less stationary. The histogenesis of these organs, hoAvever, is not yet quite settled. §238. The pituitary body, or hypophysis cerebri, Avas formerly supposed to be a glandular structure, but Avas subsequently classed among the nervous organs. Present in all five classes of vertebrata, but smallest in man and the mammalia, it consists in the latter of two portions or lobes. In the smaller posterior part, which is greyish in colour, we meet in a connective- tissue substratum with fine isolated nerve tubes, cells resembling ganglion corpuscles, a quantity of sustentacular connective-tissue, Avith fusiform cells and blood-vessels, but no glandular elements. The anterior lobe, much larger and redder, has by no means the same structure. It is traversed by a canal according to Peremeschko, and, as Avas found many years ago by Ecker, it possesses great similarity Avith the so-called blood-vascular glands. Here Ave encounter, within a connective- tissue framework very richly supplied Avith blood-vessels, roundish or oval glandular cavities, measuring in man and among the mammalia 0*0496- 0*0699 mm. These are occupied by cells of about 0*0140 mm. in diameter, with tolerably large and finely granular bodies. Here also Ave find, according to Ecker and Peremeschko, a colloid metamorphosis of the cells, like that Avhich takes place in the thyroid gland. The canal, Avhose form is very various in different animals, is lined among the latter with flattened cells, which in man are ciliated. It is continuous Avith the ORGANS OF THE BODY. 447 cavity of the infundibulum. Behind the canal the glandular tissue assumes a somewhat different character. Here we remark besides a finely granular mass and free nuclei, cells, whose bodies seem poor'in granular substance. Colloid vesicles are also to be found here; the frame- work is formed of a somewhat more highly developed connective-tissue than elsewhere. o ,-Sn Pituitar^ ^ody is richly supplied with interlacing capillaries, 0*0050 mm. m diameter, the anterior portion being most vascular (Peremeschko). Some years ago an extraordinary little organ, of roundish figure, and about 2 mm. in diameter, was discovered by Luschka, which, owing to its position on the tip of the coccyx, he named coccygeal gland. The structure of this body, as described by the dis- coverer, resembles, if Ave except several peculiarities, in general that of the blood-vascular glands, namely, the hypophysis cerebri and suprarenal capsules. The subsequent researches of Henle, Krause, and Koelliker, have not shown any essential inaccuracies in his description. Like the pituitary body, the coccygeal gland is placed at one extremity of the sympa- thetic chain; and, like the suprarenal capsule, it is rich in nervous elements. As gland- ular elements, it is stated to contain round vesicles and simple and branching follicles, imbedded in a tolerably solid connective-tissue interspersed with numerous elongated nuclei. The coccygeal gland, which is very vascular, receives its blood from a branch of the sacral is media. The accuracy of this description has, hoAvever, been recently questioned by J. Arnold, in toto. According to him, the organ does not-contain glandular elements, but belongs rather to the vascular system, being composed of a multitude of saccules communicating Avith the arterial twigs of the part (fig. 430, b, c). When strongly marked these may form a system of convoluted diverticula, recalling to our minds the glomeruli of the kidney, and possessing ahvays the same structure as the walls of arteries, Avith a strongly developed external layer of longitudinal muscle fibres (h, i). Groups of these saccules may open immediately into the arterial tAvigs (a), and are like them filled Avith blood ; they may, however, owing to the fineness of the afferent and efferent blood-vessels (d, e,f), appear to be completely closed on all sides. These statements have, however, been again questioned. The glandular structure of the organ has once more been insisted on, the cells supposed by Arnold to be Fig. 430.—Vascular diverticulum, b, c, of the coccygeal gland lined with endothelium; a, afferent, d, efferent arterial twig; e. f, branches which break up into a capillary netwoik; h, i, muscular tissue; g, envelope (after Arnold). 448 MANUAL OF HISTOLOGY. endothelium, are regarded noAv as covering vessels situated in its in- terior. The so-called ganglion intercaroticum, which was found by Luschka to be very similar, as regards its microscopical appearance, to the coccygeal gland, has also been declared by Arnold to have the same peculiar vascular structure as the latter. 2. Respiratory Apparatus. § 239. The respiratory apparatus is made up of a system of branching canals for the entrance and exit of air, and a proper respiratory part. The first of these is represented by the larynx trachea and its ramifications, the latter by the lungs. The whole may be compared to a racemose gland. It presents important peculiarities as well physiologically as anatomically, and especially in the high development of its elastic tissue. The larynx consists, Ave know from descriptive anatomy, of several cartilages, the ligaments connecting these one Avith another, the muscles by which they are moved, and a lining of mucous membrane. In describing cartilaginous tissue we have already referred to the various cartilages of the larynx. These afford examples of the different species of this tissue. The thyroid, crycoid, and arytenoid are formed of hyaline substance. At certain points in the latter, however, namely, in the processus vocalis and apex, a change into elastic cartilaginous tissue has already commenced (§ 107, p. 176). The cartilages of Wrisberg and Santorini, and the epiglottis, are entirely formed of the latter tissue (§ 108, p. 180), while the c. triticea appear to be principally composed of fibrous tissue (§ 109, p. 181). The ligaments of the larynx are either almost entirely composed of elastic fibres, or are at least very rich in them (p. 229). Those in Avhich the essentially elastic nature is best marked are the vocal cords, the ligamenta thyreo-arytcenoidea inferiora. The muscles of the larynx belong to the striped class (§ 164, p. 103). The epiglottis is in the human subject covered on its anterior surface with a strongly laminated epithelium 0*2 or 0*3 mm. in depth, and on its posterior aspect with a much thinner bed, only 0*06 or 0*1 mm. The loAver part of the latter is lined Avith laminated ciliary epithelium 0*15 mm. or even more in thickness. The mucous membrane, Avhich, especially in its deeper portions, is rich in elastic tissue, presents as a rule a smooth surface and tough texture. At certain points, however, it presents larger or smaller papillar, as on the true vocal cords. Its most superficial layer contains lymph cor- puscles embedded in it close under the epithelium. These may be pre- sent in such number as to give rise to regular lymphoid follicles, single or grouped. Finally, it is studded with numerous racemose mucous glands, either scattered or crowded together in certain situations. The bodies of these glands may lie embedded in depressions in the subjacent cartilage. It is by these organs that the mucus of the larynx is secreted. Their excretory canal appears thick-Availed, and the acini are frequently elongated and clothed with low columnar cells. From the base of the epiglottis and false vocal cords the epithelium (with the exception of that clothing the true cords. Avhich is of the ORGANS OF THE BODY. 449 laminated flattened species) consists of a slightly laminated layer of cili- ated cells (1) (p. 149). Among these are scattered a certain number of beaker cells, which are also present in the trachea and its ramifications, according to Gegenbaur and Knauff. The nerves supplying the larynx are branches of the vagus, namtdy, the laryngeus sup>erior, composed of fine medullated fibres principally sensitive, and the I. inferior, formed of broad filaments, and essentially motor. Their ramifications have in many cases microscopically smail ganglia connected with them. They are distributed to the muscles, the perichondrium, and the mucous membrane. Their terminal plexuses may be recognised in the latter, but not the ultimate ending of their primitive fibrillae. Nothing unusual is to be seen in regard to the blood-vessels. The lymphatics are numerous, and are arranged in the mucosa and sub- mucous layer in a superficial and deep network, Avhich are not, however, sharply defined against one another in all cases (Teichmann). §240. The trachea, Avith its branches the bronchi, may be described as a ramifying tube, consisting of a strong fibrous tissue, in whose anterior Avail lie embedded the annul/' cartilaginei. Thus the fibrous tube pre- sents in the first place perichondrium, and then the ligamenta interan- nularia connecting the half rings of the trachea one wdth the other, and finally closing the cartilaginous canal behind the membrana transversa. The latter is strengthened internally under the mucous membrane by a thick layer of muscular bundles, running for the greater part transversely. The fibrous tissue of which the canal is principally formed possesses besides an abundance of elastic fibres (p. 229). The tracheal cartilages belong to the hyaline species (§ 107), and have nothing remarkable about them. The muscular substance of the wind-pipe is made up of smooth fibres (§ 163). It is about 0*8-1*2 mm. thick. The great abundance of elastic tissue present throughout the whole respiratory apparatus, aUows also of the formation of beautiful elastic tendons, through Avhich these muscles are attached to the perichondrium on the extremities of the annuli cartila- ginei. External to these transverse muscular fibres there are frequently, though not invariably, found a number of scattered longitudinal bundles which take their rise from the fibrous wall of the canal (Koelliker). The mucous membrane of the trachea, 0*13 or 0*15 mm. in thickness, contains a multitude of racemose mucous glands, in some instances small and simple, in others large and complex, in Avhich case the body of the organ reaches deeper into the Avail of the tube. The larger glands are situated partly betAveen the rings of the trachea, and partly in the pos- terior wall, in which a regular layer of them presents itself. The surface of the mucous membrane is clothed Avith ciliated epithelial cells, of 0*0594 mm. in height, interspersed with beaker cells. The trachea is also richly supplied with blood-vessels and lymphatics. The latter are arranged in a superficial layer of minute canals, measuring in diameter 0*0678 mm., lying in the mucosa, and taking principally a longitudinal direction, and a deeper set of much larger tubes 0*0941 mm. in diameter. The course of these stronger trunks is, at least, partly transverse (Teichmann). The nerves of the part which are supplied by the sympathetic and inferior laryngeal require closer study. 450 MANUAL OF HISTOLOGY. §241. We turn now to the consideration of the lungs. These organs may, as regards form, be compared to racemose glands. This resemblance is also seen in their mode of development. The excretory canals are represented by the bronchial ramifications, and the acini by the air-vesicles. Besides these numerous blood-vessels, lymphatics, nerves, and connective-tissue structures enter into their composition. The two bronchi, which, as is wed known, divide again into two before their entry into the roots of the lungs, continue to sub-divide Avith the factor two, and at acute angles, on entry into the organ, so that a multitude of ever decreasing canals is soon formed. The cartilaginous supports lose from this on the character of rings, and assume rather the form of irregular plates and scales, which are no longer confined to the anterior wall, but for the rest, as far as their texture is concerned, differ in no respect from those of the trachea. The last traces of cartilaginous plates are only lost in bronchial twigs of extreme fineness, Gerlach having found them in those of only 0*23 mm. diameter. The walls of these tubules present, but in decreasing strength, of course, the same fibrous layer that we have already seen in the trachea, and a mucous membrane with ciliated cells, which loses gradually its laminated structure, until there only remains at last but one single layer, 00135 mm. in height, of dwarfed cells (p. 149). Racemose mucous glands, likewise, present them- selves here until we pass into canals of extreme fineness. The smooth muscular layer which, as we have seen in the foregoing section, exists in the trachea, forms around the bronchial passages a continuous tunic. It may be folloAved here, likewise, down to the very finest tubes, and is present possibly even in the neighbourhood of the air- vesicles, but is certainly not to be found on the latter. In the very finest tubes the mucous membrane and external fibrous layer become eventually fused into one single thin coat, made up of a homogeneous membrane surrounded externally by elastic fibres. Owing to this progressive sub-divi- sion, together Avith which small lateral twigs are given off from the larger bronchi, a very complex system °of branching passages is produced. At the end of the last bronchial twi^ (fig. 431, a), tubes of 0*3-0*2 mm. tn diameter, Ave come upon the true re- spiratory part of the organ. This con- sists, in the first place, of thin-walled across. To these the name of alveolar Fig. 431.—A portion of the lung of an ape (Cercopithesus) filled with quick- silver (after F. E. Schulze). a, end of a bronchial twig; c, alveolar passage; b, infundibula. Hig 432. —Two primary pulmonary lobuli or infundibuli (a) with the air-vesicles, 6; and terminal bronchial tubes, c; which also bear some of the pulmonary ve- sicles, 6. round canals of 0*4-0*2 mm. ORGANS OF THE BODY. 451 passages has been given by Schulze (fig 431, b; 432, c). They are sub- divided again at acute angles, and end finally in peculiar dilatations (431, b; 432, a). These are the so-called primary pulmonary lobules. They are of short conical figure, and have received from Rossignol the name of infundibula. These primary lobuli correspond, to a certain extent, Avith the primary lobules of the racemose glands, and are like them made up of terminal vesicles, as a rule roundish, but polyhedral when strongly distended. They are always met with on the surface of the organ in this form. There is, however, a difference between the tAvo. While the saccules, namely, of every genuine racemose gland remain more or less distinct from one another, the analogous parts of the respiratory organs, to which the names air cells, pulmonary vesicles, alveoli, or Malpighian cells, have been given, are far less isolated. They appear to be rather saccular dilatations in the walls of the primary lobules, in which no further canals are to be discovered, all the alveoli, on the contrary, opening Fig 433 —Transverse section through the substance of the lung of a child of nine months (after Ecker) b a number of air vesicles enveloped in elastic fibrous networks which, together with a thin structureless membrane, form the walls of the same; d, a portion of the capillary network of the part, with its tendril-like tubes projecting into the cavities of the alveoli; c, remains of epithelium. directly into a common cavity. In the adult body, moreover, absorption of the walls betAveen the several air cells of an infundibulum may take place (Adriani). . The side walls of the alveolar passages are also thickly covered with numbers of similar pulmonary vesicles (fig. 431, c, c). In sections of pulmonary tissue (fig. 433) the more or less round or oval form of the vesicles may be recognised in the open spaces of varying size brought into view (b), agreeable to the description just given The diameter of the alveoli is generally stated as ranging between 0*1128 and 0*3760 mm. Their great elasticity admits, of course, during life, of their dilatation to a great degree, so that, as we Avould expect the vesicles are, at the end of inspiration, much larger than during expiration. 452 MANUAL OF HISTOLOGY. Complete collapse or distension of the air cells, hoAvever, never takes place under normal conditions in the lung. The possibility of this is pre eluded by the situation of the organ. This, namely, is hermetically sealed up Avithin the cavity of the chest. On account of its distensibility, there- fore, it follows all the motions of the thorax in inspiration, most accurately lying in contact Avith every part of the internal surface of the latter. Then, on account of its elastic nature, and aided by the muscles of its air passages, it contracts with every expiration as much as is admitted of by the walls of the chest. It never, hoAvever, goes so far as entire collapse, which is only reached naturally when the cavity of the thorax is laid open, on Avhich it at once takes place. If we now inquire into the texture of this elastic alveolus, Avhich is constantly expanding and contracting during life, Ave will find a feAV points elucidated by fig. 433. The Avails of the air vesicles, as continua- tions of the finest bronchial ramifications, present for our consideration, in the first place, an extremely delicate membrane of connective-tissue, measuring about 0*0023 mm., and less, in thickness. At the right side of the plate a portion of this may be seen in the large central alveolus. This very fine membrane serves to connect the croAvded capillaries of the walls, and probably clothes the surfaces of the latter. We require, how- ever, further research on this point before it can be established. This membrane of the air cells is then covered externally by a greater or smaller number of elastic fibres, varying greatly as to thickness. They present themselves either scattered or in groups. The strongest fibres are to be seen in the interalveolar septa, especially betAveen adjacent vesicles, closely packed together. The remaining portions of the alveolus are poorer in them than the entrance, and especially tho fundus. Here are to be seen, scattered at Avide intervals, the most delicate elastic elements, measuring perhaps 00011 mm., and appearing like reticular connections between the air vesicles. The limiting membrane, on the other hand, does not appear to possess many nuclei, most of those Avhich are to be seen probably belonging to the capillaries or epithelia. These primary lobules of the lung, best studied in the infant, the structural relations often becoming very indistinct in the adult, enter again into the formation of the secondary lobuli, connected together through the medium of connective-tissue. The diameter of these latter may be roughly estimated at 1 or 2 mm. They are more distinctly seen in the adult than in the infant, in the form of polygonal fields on the surface of the organ, marked out by the deposit between them of black pigment. By the aggregation of these lobuli the larger lobes are gradually formed, the consideration of Avhich belongs to descriptive anatomy. It is a curious feature in the existence of the interstitial connective- tissue of the lung, that there is usually a certain amount (frequently very large) of black pigment deposited in it. The Avails of the air vesicles, also, may likewise be affected in the same way; besides which, molecules of this substance are met with in the protoplasmic bodies of the smaller epithelial cells of the respiratory tubes, and in certain rounded corpuscles connected with the mucus of the part. We have already referred to the pigmentation ofthe bronchial glands (p. 418). It was for a long time supposed that this pigmentation resulted from a deposit here of true melanin. But from the fact of its not being present in the lungs of wild animals, while in man, living in an atmosphere of ORGANS OF THE BODY. 453 smoke, and loaded with soot, it is found in large quantities, it Avas inferred that the true origin of the pigmentation must lie in the inspira- tion of particles of carbonaceous matter. This view seems to be confirmed, farther, by observations made on the organs of those engaged in occupa- tions which necessitate their breathing an air charged with supended dust of various kinds, as, for instance, those of coal miners, whose lungs may be found to be perfectly black. It was also discovered that large frag- ments of Avood charcoal often make their way into the air vesicles, and that the lungs of animals, when confined in sooty chambers, become quite black (Knauff). That a deposit of genuine melanin, however, does also take place in the lungs and air passages, as Avell as in the bronchial glands, is beyond doubt, but we are unfortunately unable as yet to dis- tinguish betAveen the t\vo kinds of particles. Remarks.—A distinction betwee-n " anthralcosis " and "melanosis" of the respira- tory organs may be made. The cells which we have given in fig. 95, frequent con- stituents of the sputa, are in many instances genuine melanin cells ; but in other cases whicli may be set down as more the rule, the contractile body of the cell has taken up fine carbonaceous particles from without. "We must confess, however, that the deposit of these matters in the interstitial connective-tissue of the lung and parenchyma of the bronchial glands is still a subject of great obscurity. §242. There now remain for our consideration but a few more structural relations in dealing with the lung. There are the arrangement of its blood and lymphatic vessels, epithelium of the air vesicles, nerves, and serous covering. The blood-vessels of the organ receive their blood, as is well knoAvn, from two sources: firstly, from the bronchial; secondly, from the pul- monary arteries. The first of these serAre the subordinate purpose of yield- ing nourishment to the tissue of the organ ; the second are set apart for the requirements of respiration. The distinc- tion between the two, however, is by no means sharp. The arteria pulm.onalis divides and sub- divides, following the ramifications of the bronchi, and arrives thus Avith its twigs between the lobuli. Here a further split- ting up occurs until very fine tubes are formed, which penetrate into the elastic band-work between the pulmonary vesicles (fig. 434), often sub-dividing still further in their course here. At the same time, the most extensive anastomosis takes place, so that imperfect or even complete rings are formed (b). From these a multitude of capillary tubes is given off to form the respiratory capillary network, Avhich clothes the Avails of the air-vesicles, only separated from the atmospheric air by the most deli- cate membrane. This network (a) is remarkable for the great regularity and small size of its meshes. It may be reckoned among the densest, as also the most regular occurring in the body. The peculiar form of its wide -capillaries is also striking. The diameter of the latter is about 0*0056-0*0113 mm.. Fig. 434.—The respiratory capillary net- work of a horse's lung, injected after Gerlach's method, b, the end branches of the arteria pulmonahs encircling more or less the several pulmonary vesicles; a, the capillary system. 454 MANUAL OF HISTOLOGY. bein-** sufficient to allow of the easy passage of the blood-cells. When the pulmonary vesicle is contracted, or but very slightly distended, they appear too long for the extent of surface to be covered by them, and pro- ject in the form of loops and tendril-like convolutions, pushing before them a portion of the delicate lining membrane of the alveolus (fig. 433, d). But when the air-cells are strongly distended, these capillaries assume a much straighter direction, while the loops and projections into the vesicles disappear in a corresponding degree. In muscle, also, which is constantly undergoing change in length, we find the same' provision of nature. When contracted the longitudinal tubes of its capillary netAvork assume a spiral course; Avhen relaxed, on the other hand, they appear straight. As to the Avails of the capillaries, there is nothing remarkable about them. They are usually nucleated, and may easily be resolved into the well-known vascular cells (fig. 356, p. 363). The meshes bounded by these tubes are very close, even in lungs which have been previously inflated (figs. 433, 434, 435). They may be more or less round or angular. They have a diameter of from 0*0393 to 0*0293 mm. That in the uninflated organ the meshes will be found much Miialler than in the inflated, owing to their shrinking together, is quite evident. The capillaries, further, of adjacent alveoli intercommunicate very exten- sively. But the fine twigs of the pulmonary artery also, curious to say, form in another situation a wide-meshed capil- lary network, namely, under the pleura. Here they communicate with the terminal tubes of the bronchial arteries. The pulmonary veins take their origin from the capillary netAvorks just described, with scattered tAvigs in the interalveolar septa. The con- fluence of these produces larger trunks, Avhich accompany the bronchi and ramifications of the pulmonary artery back to the root of the organ. The bronchial arteries, giving off as a rule a single branch to each of the air passages, supply numerous tAvigs in the root of the lung to the larger vascular trunks, the lymphatic glands of that neighbourhood, and the connective-tissue between the lobuli and under the pleura. In the walls of the bronchi and their ramifications they are resolved into an external loose network of capillaries for the muscular tissue of the part, and an internal and much denser for the mucous membrane. In the latter, hoAvever, there is, besides, another coarser and more superficial capillary network, which does not appear to communicate in any way with that of the bronchial arteries. It belongs to the respiratory system proper, and may he injected easily from the vena pulmonalis, Avith diffi- culty from the arteria pulmonalis, and not at all from the bronchial arte- ries. From this we may infer that its radicals spring from the respiratory capillary network (Henle). The arrangement of the bronchial veins, further, is peculiar. These pro- Fig. 435.—Pulmonary vesicle from the calf, a, large blood-vessels traversing the septa of the alveoli; b, capillary network; c, epithelial cells. ORGANS OF THE BODY. 450 bably only receive the blood returning from the thick walls of the larger bronchi, and from the lymphatic glands and pleura around the root of the organ. The finer and internal venous radicals, on the other hand, coming from the smaller divisions of the air passages, and which corre- spond to the distribution of the bronchial arteries, empty themselves into the branches of the pulmonary veins. Lymphatics, as has long been known, are present in the lungs in con- siderable number. They may be divided into tAvo classes: into super- ficial (arranged in retiform interlacements immediately under the serous covering of the organ); and into deep, Avhich may be traced outwards along the air passages into the bronchial glands. Both of these sets of vessels communicate freely, hoAvever, with one another. Not long since Wywodzoff was fortunate enough to succeed in injecting the radicals of the lymphatics in the walls of the alveoli in the lungs of the dog and horse, and Sokorsky also in the first named animal and in the cat. In these Avails are found lacunar, which are enlarged opposite the meshes of the capillaries. They cross the capillaries, without, how- ever, forming sheaths of any kind around them. Soon after, hoAvever, the lymphatic canals as they pass away commence to occupy the adven- titia of the blood-vessels. We now come to the considera- tion of the epithelium of the air- cells—still a subject of controversy, and Avhich has been recently the object of the most earnest investiga- tion. Turning then, in the first place, to the lung of the frog, Ave find the arrangement of parts of the simplest kind (fig. 436). The whole respiratory portion of the organ is lined Avith a single continuous layer of flattened nucleated epithelial cells. But the"lungs of the mammalia and man present greater difficulties. _ Here we must first study the structure of the parts at an early period of existence, if we would understand it in the adult body. In the mammal foetus we likewise find a continuous epithelium lining both pulmonary vesicles and alveolar passages, and entirely the same in both. Its elements are flat polyhed- ral cells, Avith nucleus and protoplasm. After birth, however, several changes become rapidly apparent, consequent upon the commencement of respiration. Only a small portion of the epithelium preserves its former character. Over the projections of the capillaries, and all other promin- ences, we can find much larger pale cells without protoplasm or nucleus in many cases. 30 Fig. 436. -A portion of an air-cell from the lung of a frog. Fig. 437. 456 MANUAL OF HISTOLOGY. Fig. 437, after an old drawing, represents the original cells in the meshes of the capdlary network of a young animal. The condition of parts, on the other hand, in the mature mammal, is •riven in li**'. 438. Here large non-nucleated plates are seen, with remnants of the original small cells, and a trace of the protoplasm and nucleus with them, at their points of contact and corners (Schulze). The nerves of the organs of respiration spring from the anterior and posterior pulmonary plexus. They are derived partly from the sym- pathetic and partly from the vagus, and take the same course, to a great extent, as the ramifications of the bronchi or the pulmonary arteries. Fig. 438.—Epithelium from the base of an infundibulum situated immediately under the pleura. From a fully-grown cat; treated with nitrate of silver. The pulmonary veins aud bronchial arteries are not accompanied to the same extent by nervous twigs. On the external surface of the bronchi there are to bo found, in connection with the latter, numerous small ganglia (Remak). The same are seen on the finer ramifications of the nerves in the tissue of the lung (Schiff). These nervous filaments appear to ter- minate in many cases in the mucous membrane of the bronchi. The pleural covering of the lung and thorax presents, as far as epithe- lium and connective-tissue substances are concerned, the ordinary texture of all serous membranes. The nerves of the structure are derived from the phrenic, vagus, and sympathetic (plexus pulmonalis). Those distri- buted to the pulmonary pleura are stated by Koelliker to have scattered ganglion cells among them. The vascularity of the membrane is low, the capillaries being very fine, and forming wide meshes. The pulmonary pleura receives its vessels, as has been already mentioned, from the pul- monary and bronchial arteries. The lymphatics of this membrane are to some extent Avell known, espe- cially from the recent studies of Dybkowsky. In the dog they are only evident in the movable portions of the parietal layer, i.e., in the inter- costal spaces, and upon the sterno costalis muscles, but not upon the ribs. On the mediastinal portion they are only seen at those spots Avhere col- lections of fat-cells exist. ORGANS OF THE BODY. 457 The lymphatic network is very dense, and may be divided into two layers separated from one another by fibrous tissue. The superficial canals traverse the interstices of a reticulated layer of connective-tissue, the substratum of the serosa. Here their walls, composed of vascular cells, are covered solely by the epithelium of the membrane between whose cells those orifices already described in section 208, fig. 381, 2, 3, are situated. Absorption from the cavity of the pleura is effected through the agency of the respiratory movements in the intercostal spaces, and the varying amount of tension to which the connective-tissue in Avhich these canals are situated is subjected thereby. The contents of the networks formed by the latter are received by valved vessels running along the ribs toAvards the vertebral column and by the mammary twigs. §243. Turning noAv to the composition of the pulmonary tissue, we find that only of the products of decomposition occurring in the fluids with Avhich Cloetta obtained inosite, it is saturated is anything really known. taurin, and leucin from the lung of the ox. The human lungs, also, Avere found to con- tain leucin in considerable quantity. In the foetus the organ yields glycogen (Ber- nard, Rouget). The development of tho lungs (fig. 439, 1) takes place very early in the same way as the large glands connected Avith the intestinal tube, namely, in the form of two holloAV processes (c) attached by one stalk (a) to the anterior wall of the pharynx. This body is hollow from the very commencement. Both the internal and middle germinal plate are here represented, the former in the cellular layer (c), the latter in the fibrous wall of the part (b). From the cellular layer the epithe- lium of the respiratory tract is derived, Avhile in the ex- ternal investing mass we have the rudiments of all the fibrous and cartilaginous por- tions of the air-passages, bronchi, and lungs. From these blind tubes of the glandular plate an ever-increasing number of new sncculi (d) are now given oft into tne surrounding substance by means of cell-multiplication, so that the arbores- cent arrangement of the respiratory canals becomes more and more marJcel, as the enveloping layer decreases progressively in proportion. At tlie Fig. 439.—Development of the lungs. 1. Plan of the for- mation of the whole organ, a, common canal (the future trachea) dividing into (c) the two bronchi, with their incipient bud-like saccules, (d); b, the surrounding fibrous mass. 2. Ramifications farther advanced, from the lung of a human foetus about four months old. a, the tube; 6, lobulated dilatations lined with cylinder epithelium, from which the infundibula are formed appa- rently. 3. The same strongly magnified, a, cylinder epithelium; c, cavity; b, the investing fibrous layer, the remainder of b, fig. 1. 458 MANUAL OF HISTOLOGY. ends of the branches (2, a) there then appear round vesicular dilatations (b), lined with cylindrical cells (3, a), which by a process of gemmation are resolved into a number of finer loculi, from which then the infundi- bula or primary lobules are derived, and in all probability also their air- vesicles by a further sacculation of their walls. The pulmonary tissue is subject to many changes One senile meta- morphosis consists in the disappearance of parts of the alveolar walls, and confluence of the air vesicles to form larger cavities with consequent destruction of the capillaries contained in the interalveolar septa. The occurrence of new growths here is an obscure subject, especially as regards their point of origin. This may probably be the nuclei ot the vascular cells, or the epithelium of the lung. 3. The Digestive Apparatus. §244. The digestive apparatus consists of the mouth Avith its teeth, .already described °§§ 150 and 156, the tongue, and attached salivary glands, then of the pharynx, oesophagus, stomach, large and small intestine, the large glands emptying their secretions into the upper portion of the last of these, namely, the pancreas and liver. Almost every variety of tissue takes part in the formation of this extensive group of organs, in AA-hich the glandular elements espe- cially are pre-eminently important, and are found from the upper to the lower aperture of the alimentary canal forming a mucous covering for the whole internal surface. The cavity of the mouth is lined by a mucous membrane of thetexture roughly described already (§ 136), which is marked on its free surface by a multitude of closely crowded conical and filiform papillae (fig. 440). The thickness of this mem- brane varies, its maximum being sometimes 0*45 mm. The papillae likewise differ greatly in length, rang- ing from 0*23 mm. to 0 45 mm. The strongly laminated epithelial layer consists of flattened cells (fig. 444), which we have already considered at greater length at p. 141. At the opening of the mouth they are con- tinuous with the cells of the epidermis. This mucous membrane itself is rich in elastic fibres, and presents a network of connective-tissue bundles. It is denser towards the surface, upon which a homogeneous transparent limiting layer may be seen. In the papillae here, as in those of the external skin, and still more in the villi of the intestine, the connective-tissue loses its fibrous character more or less, and presents itself in a rather undeveloped form. Below, the mucous membrane gradually merges into submucous tissue. The latter is in some localities a solid fibrous mass, as in the case of the gum, and in others soft and elastic, with loose texture, as on the floor of Fig. 440.—A papilla from the gum of an infant, with its vascular network and epithelial cover- ing. ORGANS OF THE BODY. 459 the mouth. In this substance are to be found globular groups of fat cells and the bodies of mucous glands. The last named organs (fig. 442) present themselves in large numbers in the mucous membrane of the mouth. They measure in diameter from 4*5 and 2*3 down to 0*5640 mm., or even loAver, and are usually situated in a row underneath the true mucosa, where they may be so closely :*/f|£*V •■.•IS*.*!.-; *.. ' '&'■ . Fig. 441.—Epithelial cells from Fig. 442.—Racemose mucous glands the most superficial layers of from man (so-called palatal glands) the mucous membrane of the human mouth. croAvded as to form a regular special glandular stratum. From this their short and more or less straight ducts penetrate the mucous membrane, and open on the surface. Their structure is as elseAvhere : for which see sections 198 and 197. In certain localities these little glands, Avhich play an important part in the production of the mucus of the mouth, are particularly numerous, and then receive special names. Such are the labial, buccal, and palatal. The first of these, Avhich are very numerous, form, at some little distance from the red margin of the lip, a regular group. They are most numerous in the under lip (Klein). Their cells usually present them- selves in the form of numerous Ioav, clear, columnar elements, but slightly coloured by carmine, as was very correctly described by Puky Akos. According to Heidenhain, hoAvever, there occur also (in man and the rab- bit) other smaller elements, richer in protoplasm, from the transformation of Avhich the first take their rise. The little palatal glands, likewise, are arranged in a thick pad under the mucous membrane of the soft palate. The vascularity of the mucous membrane of the mouth is very great, the capillaries forming a close network. In the papillae Ave encounter either a single loop or congeries of vessels (fig. 440). We are still to a great extent in the dark as to the lymphatics. So much is known, hoAv- ever, that they interlace along the lips, the inner surface of the cheeks and the tongue, and covering the glands of the mouth, form interlace- ments, Avhich communicate with the vessels of adjacent parts (Teichmann). The final distribution of the nerves of the mouth is a point on which even less is knoAvn. Krause observed end-bulbs upon them (§ 184), in the furrows of the mucous membrane on the floor of the mouth, near the tongue, in the soft palate, and in the tissue of the membrane, at the edge of the red margin of the lips, but not always in the papillas. Elin states, on the other hand, that both in the hard and soft palate of the rabbit, fine nerve filaments penetrate into the epithelium, and (§ 245) terminate in ramifying cellular bodies (§ 187). 460 MANUAL OF HISTOLOGY. §245. Until very recently, the salivary glands received but little attention from a histological point of view, but a step in the right direction has lately been made in the interesting studies of Pfiuger, Gianuzzi, and Heidenhain, followed by a number of other observers. These organs may from their form be regarded, to a certain extent, as highly developed and complex mucous glands. The submaxillary gland presents in various mammals, according to its cellular contents, considerable and important physiological differences. Its vesicles in the rabbit are occupied by closely croAvded naked cells, consisting of soft protoplasm. The organ in other animals—as, for instance, the dog (fig. 443), the cat, and in a minor degree, the sheep— departing from this form, have all the characters of a mucous gland. Here the greater part of the vesicle is filled with large, clear, non-granular cells, with a nucleus which is usually situated near the circumference (a). Besides these, Ave may see in the greater number of vesicles, close to the border of the latter, a peculiar element usually of semicircular form, and either single or double, the "crescent" of Gianuzzi (c). At first this appears to be a granular mass of protoplasm with imbedded nuclei, but after being subjected to a particular kind of treatment, it may be recognised to be a collection of small highly compressed cells. Other saccules contain protoplasm cells alone (b). These crescents reach the highest stage of development in the submaxillary of the cat. The first of these elements—we shall give them the name of mucous cells—present, after maceration, the most remarkable irregularity of outline. They may, however, discharge their mucous con- tents, as we shall see later on, and then present protoplasm only. Intermediate forms teach us that these mucous cells are not specifically different from those of the crescent, or border cells, but only so on account of their having become altered and un- dergone mucous metamorphosis. In newly born animals they are not yet to be found. The submaxillary glands of man, like- wise (specific gravity of 1*041, according to Krause and Fischer), contain the same mucous cells, which require, however, closer investigation. For a long time it was main- tained that the submaxillary gland possessed, most unquestionably, a structureless membrana propria. More recent investigations, however, have shown that the boundary layer is only formed of greatly flattened cells of stellate figure, which probably belong to the connective-tissue group (Heidenhain, Koelliker) §194. 'ii Fig. 443.—Submaxillary gland from the dog. a, mu- cous cells; b, protoplasm cells; c, "crescent" of Gianuzzi; d, transverse section of an excretory duct with its special columnar epithelium. ORGANS OF THE BODY. 461 We have already referred (p. 350, fig. 339) to a network of fine secreting tubules or canaliculi, which have been met with in the acini of many racemose glands. These are also to be found in the submaxil- lary glands (Pfiiiger, Ewald, and others). Even uninjected, they can be recognised as a network of clear, someAvhat lustrous, streaks of 0*002-0*003 mm. in diameter. Hoav far a recently observed connective-tissue reticulum (Boll), which traverses the acinus, has anything to say to these secretion tubules, or is connected with the wall cells of the membrana propria, are points Avhich require closer investigation. The walls of the excretory duct are made up of connective-tissue. A thin layer of muscular cells, difficult of recognition, has been stated by Koelliker to occur here ; these have not, .however, been found by others (Eberth, Henle). The epithelial lining consists of a single layer of cylinder cells (d), in whose bodies we may recognise distinct and per- sistent longitudinal markings (Pfiiiger) underneath the nucleus. The vascular networks are, as in most racemose glands, round. The capillaries lie loosely about the glandular vesicles, whde their tubes of supply and overflow accompany the ramifications of the ducts. The recent investigations of Gianuzzi have made us acquainted with the lymphatics of the salivary glands of the dog. Here they appear as clefts in the interstitial connective-tissue betAveen the lobuli and vesicles, as well as around the lobes of the organ. They are stated, also, to Fie. 414 -Mode of termination of the nerves in the submaxillary gland of the rabbit, after Pfluatr. Tn I. and II. the nerves penetrate into the gland vesicles, and end betweer»««e«"» of the latter. In III. the termination of a nerve fibre in the nucleus of a gland cell is observed. IV. the same, with a "ganglion cell." ensheath the venous and arterial twigs before becoming developed into regular lymphatic vessels. . The mode of termination of the nerves of the submaxdlary gland is very remarkable and important, though not, perhaps in some cases ascertained beyond all doubt. After some earlier studies by Krause Reich, and Schliiter, the point was taken up and pursued with much vigour by that excellent observer, Pfiiiger, taking the rabbit as subject 462 MANUAL OF HISTOLOGY. (see § 183). The following are the conclusions drawn from his investiga- tions. In the first place, medullated nerve fibres make their Avay as far as the gland vesicles, then pierce the membrana propria of the latter (Hg. 444, I.), and so get between the cells of the gland. The terminal filaments, hoAvever, advance still further (II.), penetrating into the very- body of the cells, and end in the nuclei of the latter (III.) The nerve fibres, further, are connected with multipolar cells declared by Pfiiiger to be ganglion corpuscles. These are situated on the external aspect of the membrana propria (IV.), sending their processes from thence into the protoplasm of the gland cells. Pfiiiger describes, finally, another set of fibres Avhich become resolved into pencils of the most delicate primitive fibrillae, which become fused eventuaUy with the bodies of the epithelial cells lining the ducts. These it is which produce that longitudinal striation beneath the nucleus already spoken of. For the present we defer giving any opinion as to these statements, hut must just remark that we have never been able to find anything ofthe kind, and have already described the ganglion corpuscles alone as connective- tissue cells, entering into the structure of the Avails of. the gland vesicles. But little attention has, up to the present, been given to the texture of the sublingual glands. From Heidenhain we learn that in the dog they appear to be very similar in structure to the submaxillary, and to have likewise two kinds of cellular contents, mucous elements surrounded by border cells. The groups of the latter, however, are usually larger than in the submaxillary gland, and in many instances extend around the whole circumference of the gland vesicles. Sometimes even the latter are entirely devoid of mucous cells. The interstitial connective-tissue of this gland, farther, is remarkable for the great abundance of lymphoid cells which it contains. The ducts of Bartholini and Rivin are completely destitute of muscular fibres. Comparatively little is known also about the structure of the parotid gland. In its wall we find the same flattened multipolar elements already mentioned in speaking of the submaxillary organ. The diameter of the gland-vesicles is 0*0338-0*0519 mm., and the granular cells contained in them 0*135-0*0180 mm. Mucous metamorphosis of the latter is never met with, however, either in man or the lower animals. Their excretory ducts are lined with ordinary epithelium, none of that fibriUation of the lower half of the cells being seen here which is to be found in the sub- maxillary gland. In the interior of the parotid, and several other race- mose glands, possibly also in the submaxillary of many mammals, the commencement of the excretory canals is formed of a different species of cells, the so-called " centro acinal" cells first discovered by Langerhans in the pancreas (see below). These are flat elements resembling vascular epithelium usually of spindle or more rarely stellate figure. They bound an axial canal of the acinus more or less perfectly. According to Pfiiiger the termination of the nerves is the same, as in the submaxillary gland of the rabbit. The development of the salivary glands is on the same plan as the race- mose. They commence to be formed in the human embryo in the latter half of the second month. They are then seen as solid aggregations of cells from which they are developed by gemmation. At thetiiird month they are already pretty Avell marked. ORGANS OF THE BODY. 463 §246. The saliva, as found m the human mouth, is a very complex mixture of the secretions of different organs connected with that cavity. In the first place of the matters produced by the numerous little mucous glands already described § 244, then of those secreted by the parotid submaxillary and sublingual glands. Under certain circumstances, also, the secretions of the mucous membranes of the nose and lachrymal gland are likewise mixed Avith it. We shall first enter upon the consideration of the variety of composition of this fluid as a whole, and then turn to Avhat has up to the present been ascertained in regard to the individual secretions from a physiological and chemical point of view. The saliva, taken as a whole, is a colourless, slightly clouded, and some- what viscid fluid without either odour or taste.. Its reaction is generally alkaline or neutral, more rarely acid. Its sp. gr. ranges between 1 004 and 1*009. Under the microscope this fluid is found to contain cast-off epithelium, and at times gland cells which have been Avashed out of their original position. As a third and never absent element, we meet Avith great numbers of what have been named salivary corpuscles (mucous corpuscles). The latter present the same appearances as lymph cells Avhich have become swollen in water. Within their bodies, as long as they are uninjured, a lively movement of small molecules may be perceived. This motion Avas always regarded as of the ordinary molecular species, until lately, Avhen Briicke came forward to oppose the theory. Turning to the chemical analysis of the secretion, we find that it con- tains between five and ten parts per 1000 of solid constituents. Among the organic matters the most important is a ferment combined with alka- lies or lime, called by Berzelius ptyalin insoluble in alcohol, slightly so in Avater. It has not yet, hoAvever, been obtained in a pure state. Besides this, leucin is probably present (?) also mucin, extractive matters, fats, and combinations of the fatty acids Avith the alkalies. Urea has also been found as an abnormal or pathological constituent. The inorganic compounds are chlorides of the alkalies, small quantities of phosphates of the alkalies and earths, carbonates, some oxide of iron, and besides,—at least in man,—sulphocyanide of potassium (comp. § 38). We insert here an analysis by Frerichs, as a specimen of its quantitative composition. The saliva of a healthy man contains :— Water,........994*10 Solid constituents, ..... 5*90 Epithelium and mucus . . . . 2*13 Fat, ...... 0*07 Mucin and traces of alcoholic extract, Sulphocyanide of potassium, Chloride of sodium, chloride of potassium, phos- phates of the alkalies, and earths, and oxide of iron, ...... The* saliva contains of gases small quantities of nitrogen and oxygen (the latter in far greater quantities than other secretions), and abundance of carbonic acid. . . _ The amount of saliva secreted is, of course, liable to variation. Bidder 2 19 464 MANUAL OF HISTOLOGY. and Schmidt have estimated it at 1500 grammes in man, but also at a lower figure. Its action and use are, in the first place, the same as water; further, as a slimy fluid it lubricates the various matters taken into the mouth, causing them to pass the more easily into the oesophagus; and then again its action on starch (CBH10O5) is chemical, transforming the latter into dextrine (C6H10O6) and grape sugar (C6H12Ofi). It is the ptyalin alone which here acts as a ferment. Let us now turn to each of the secretions in succession of which the saliva is composed, taking first the mucus of the mouth. The amount of this is inconsiderable, if we are to judge from experiments on animals. It was found by Bidder and Schmidt to contain water to the amount of 99 per cent. In the mucus of the mouth Ave find, likewise, an abundance of form elements, flattened epithelium cells, and salivary corpuscles. Of all these secretions, that with which Ave are best acquainted is the saliva obtained from the submaxillary gland of the dog. As was shown many years ago by Ludwig, the secretion of this fluid is presided over by the nervous system. From a whole series of experimental studies, partly undertaken by Ludwig and his pupils, partly by Koelliker and Muller, Czermak, Bernard, Eckhard, Adrian, and Heidenhain, we have become acquainted Avith the folloAving points of interest. The submaxillary gland receives, first of all, branches from the facial nerve, mixed with a small contingent of the trigeminus : this is the continuation of the chorda tympani. In the second place, a number of filaments of the sympathetic enter the organ Avith the arteries. Finally, it receives nervous offsets from the submaxillary ganglion, Avhich run with the chorda through the organ, and are excited by reflex action from the tongue through the lingualis. # Irritation of the chorda tympani gives rise to the secretion of a large quantity of a strongly alkaline and non-viscid fluid, Avhose proportion of Avater is about 99 per cent. Together with this the gland becomes filled with a larger quantity of blood than usual; the pressure in the veins is increased, and the Avhole mass of the blood, leaving the organ, presents a bright red colour (Bernard), whde the temperature of the latter rises about 1° C. (Ludwig and Spiess). That this secretion is independent of the increased influx of blood is clear from the fact, that after interruption of the flow through the carotid, as wed as in a head severed from the body, it may be induced by stimulation of these nerves. Stimulation of the sympathetic salivary nerves, on the other hand, has quite a different effect (Czermak, Eckhard). Here the circulation is con- siderably retarded, and the venous blood leaving the organ is of a dark red colour. A small quantity only of a very viscid, cloudy, and strongly alkaline secretion issues from the excretory duct, containing solid con- stituents in the proportion of from 1*6 to 2*8 per cent. In the-saliva given off after stimulation of the chorda, mucin has been found Avith various albuminous substances. After irritation of the sym- pathetic it is also very rich in mucin. As far as we know, neither of these secretions of the submaxillary gland have any action on the food, with the exception of a slight power of producing sugar manifested by the sympathetic saliva of the dog. The form elements appearing in these two kinds of saliva of the sub- maxillary are of great interest. Many years ago numerous pellets of colloid matter were noticed by Eckhard in the sympathetic secretion of ORGANS OF THE BODY. 465 the dog. saliva. These are entirely absent, it is stated, in the chords The fluid excreted by the submaxillary gland contains farther, as was ^ Mb7 Hrlfmm{ m the tirSt Plac*' cast"°ff ™cous cells eitW ±°?^llh?1f ^^t1!6^1^-^,- .?h-^ by maceration and Swollen up the result of which is the production of a multitude of peculiar round thlVe:7/*P ^T' hkG dr°pS °f SOme viscid suhstaLe Besides these, saliva corpuscles are present in the secretion, i.e., small lymphoid LenSiVan°US StageS °f devel°P^eut, and which have wandered outwh the fluid. iJ^Jl? °n61°f "? i,™, SeCret°ry "eIves oi the ^maxillary gland is s^^sst7** a con8ideraUe period*the MmJrof th- comes creased. of this further pointed enhain, dinary naturally in- Another effect proceeding is seen, as was out by Heid- in an extraor- transformation Fig. 445.—Submaxillary gland of the dog with its contents, a, modi- fied by strongly stimulating the chorda tympani; b, unchanged residue; after Heidenhain. of the interior of the gland (fig. 445). In the greater number of the vesicles the mucous cells are found to have entirely disappeared, irregularly granular nucleated elements, smaller than the original cells, occupying their place. The explanation is simply this, that these cells have parted Avith their mucus, and have again become filled with protoplasm (Ewald, Rheiner). In man the saliva of the submaxillary gland contains a large quantity of mucin dissolved in an alkaline fluid, together with a sugar-forming ferment and sulphocyanogen (§ 38), Avhich latter is also found in the sub- lingual and parotid secretions. In the saliva of the lower animals, on the other hand, this compound is not to be found. The secretion of the sublingual gland has, up to the present, excited but little attention. According to Heidenhain, the organ is presided over by the same nerves as the submaxillary gland in the dog, namely, the facial and sympathetic. Stimulation of the chorda tympani causes here also an increased flow of the secretion. The saliva of the sublingual gland is an extremely tenacious and completely transparent substance, which can hardly be called a fluid. Its reaction is alkaline, and its percentage of solid constituents about 2*75. The product of the parotid finally may be increased by irritation of one of the cranial nerves, namely, the lesser superficial petrosal, a branch of the facial (Ludwig, Bernard). Stimulation of the sympathetic also has the same effect (Eckhard, von Wittich, Nawrocki). The fluid thus obtained has a much less alkaline reaction than that of the submaxillary gland. It is always thin, and never in the least viscid. The secretion of the parotid, further, has no reaction on mucin, and contains from five to six per cent, of solid constituents (Ordenstein); also albumen, and, as already mentioned in the human subject, sulphocyanogen combined Avith 466 MANUAL OF HISTOLOGY. potash or soda. According to Ordenstein, the sugar-forming ferments appear in the corresponding fluid obtained from the dog (Bidder and Schmidt, Bernard). §247. The tongue is an organ essentially muscular, but covered by a mucous membrane which, over the greater portion of the anterior part of the dorsum, is studded with a multitude of highly developed papillae supplied Avith nerves, the gustatory papillce, which constitute the Avhole an organ of sense. Leaving the greater portion of the description of its striped fibres, which have a partly perpendicular, partly longitudinal, and partly oblique direction, to general anatomy, Ave shall merely touch here on one or two points of special interest. That portion of the tongue knoAvn as its Hbro-cartilage, which occupies the middle line of the organ in the form of a thin vertical septum, cannot be numbered among the cartilaginous structures, seeing it merely consists of densely interwoven bundles of connective-tissue. At either side of this band the two genioglossi pass up into the substance of the tongue, inter- mixed, as their fibres diverge, Avith the fibres of the transversus linguce, Avhich cross the former more or less at right angles. The greater part of the substance of the organ is formed by these two muscles. The hyoglossus, with its two portions, the first of the muscles entering into the formation of the border of the tongue, passes to the lateral portion of the organ in manner similar to the genioglossus, and likewise crossed by the external fibres of the transversus on each side. The styloglossus sends its Aveaker internal division between the genioglossus and hyoglossus and as far as the fibro-cartilage. Its longer external band passes forwards on the external surface of the hyoglossus, intermixing behind the frsenum and anterior to the foremost extremity of the sublingual gland, Avith the fibres of its fellow of the opposite side. Besides these there are longitudinal bundles of muscular fibres coursing from the root to the tip of the tongue, partly on the dorsum and in part near its inferior surface. The latter are the most numerous, and go by the name of the lingualis muscle. They are strengthened anteriorly by fibres from the external division of the styloglossus. Their course is betAveen the genio- and hyoglossus muscles toAvards the tip of the tongue, where their fibres diverge, some passing upAvards and others still fonvards. The superficial layer of bundles {lingualis superior) is spread out over the whole dorsum of the organ under the mucous membrane. Those muscle bundles which are lost in the mucous membrane, such as the ascending fibres of the genioglossus in the middle line, and of the hyoglossus in the lateral portions of the organ, may be seen to bifurcate at acute angles, and terminate in the connective-tissue in conical points. The most important part, however, of the tongue is the mucous mem- brane itself. This is covered over with the flattened epithelium of the mouth (§ 90), and is, Avith the exception of having papillae, in no essential feature different from other mucous membranes. Its connective-tissue substratum is tolerably strong, and interspersed with numerous elastic fibres. It is also extremely vascular. In the gustatory portions there is no submucous tissue, its place being taken by a closely woven layer of fibrous tissue, the undermost portion of the substance of the mucous membrane. ORGANS OF THE BODY. 467 §248. While the le mucous membrane on the under surface of the tongue is quite smooth and destitute of papillae, the dorsum of the organ is covered horn the foramen caecum to the tip with innumerable gustatory papillae Of these, as is well known, there are three species, although between each kind there exist a number of intermediate forms. These three species are named respectively the filiform, fungiform, and circumvallate The papillce filiformes, s. conicce (fig. 446), are found in by far the greatest number of all. They consist of a conical base bearino- on its apex a number of thin pointed papillae, the whole presenting a tufted appearance. Ihe number of the latter varies from 5 to 15 and upwards The point most worthy of note here is the high degree of development to which the epithelial layer may attain. Very horny in texture, it presents itself in long filiform and frequently bifid shreds on the end of the papillae, causing the latter to appear considerably increased in length Together with these, examples of the same kind of papillae are met witli Avhose epithelial covering is very delicate. The vascular supply consists of single capillary loops for each of the conical papillae, with one arterial and one venous twig for each group. The mode of termination of the nerves is not yet ascer- tained. The papillae are most strongly developed along the middle of the dorsum of the tongue, decreasing in size near the edes and tip. In these situations they are in many in- stances arranged in rows, en- veloped in a common sheath of epithelium. The second form, the pa- pillce fungiformes, s. clavatos (fig. 447), are found scattered over the whole surface of the tongue among the latter variety, but most numerous towards the tip. They are remarkable for their thick coni- cal form and smooth surface, and absence of tufts, together with diminution in the thick- ness of their epithelial coat. They are elevated above the surface of the tongue with a somewhat constricted neck, and terminate above in round and blunted bulbs. The whole surface of the latter (A) is studded, with numerous conical accessory papillae (p), which are covered again by the epithelia] coating of the tongue (A, e, B, e). In this species the Fig. 446.—Two filiform papillse from man, the one (p, left) with, the other (p. right) without epithelium, e, epithelial covering, ending above in long tufted pro- cesses, /; vascular portion of the papilla, with its arterial twig a, and vein v. Copied from Todd and Bowmann. 468 MANUAL OF HISTOLOGY. C- vascular loops are far more numerous than in the first form. The nerves enter the papillae as tolerably strong twigs: the mode of their ultimate termination, however, is still undecided. According to Krause, terminal bulbs may be found here (§ 184). In the third form, finally, the papillce vallatos, s. circumvallatce (fig. 448), we have the largest of all these organs, and probably also the most important, as far as the sense of taste is concerned. In man and the mammalia generally they present many varieties. Their number is small but variable, amounting to from 10 to 15. They are arranged at the root of the tongue in a V-shaped figure. Each of the projections (^4) is surrounded by a circular ridge of epithelium (B), into which racemose glands empty themselves (Schwalbe), and supports on its broad surface a multitude of conical accessory papdlae (c) overlaid with a smooth stratum of epithelium (a). That eminence Avhich forms the apex of the V-springs from the bottom of a deep groove known as the foramen ccecum Unguis. These little organs are abundantly supplied with nerves (b b). The latter form delicate interlacements, from which the primitive tubes are given off Avhose ultimate distribution will be referred to presently. The annular folds also encir- cling the papillae are likeAvise richly supplied Avith nerves (B, b). The sources of the nervous supply of these parts are the trigemini and glossopharyngei, the ninth or hypoglossus being simply a motor nerve of the tongue. The anterior part of the dorsum of the organ is innervated by the ramus lingualis from the loAver division of the fifth nerve, and by the chorda tympani, while the posterior portion is sup- plied by the lingual branch of the glossopharyngeus, which sends its ramifica- tions into the circumval- late papillae. On both of these nerves small ganglia are to be seen. It seems hardly probable that the filiform papillae, clothed as they are with a large amount of horny epithelium, should be the recipients of the sense of taste (Todd and Bowman). The two other forms seem to preside over the latter as well as the sense of touch. The lymphatics of the tongue have been carefully studied by Teieli- mann and Sappey. According to the former, the mucous membrane, and Fig. 447.—Fungiform papilla, from the human tongue. A, a papilla covered to the left with epithelium, e, and over its whole surface with conical smaller papillae, p. B, another, less strongly magnified, with its epi- thelial envelope c, its capillary loops d, artery a, and vein v; e, vascular loops in the adjacent simple papillae of the mucous membrane. Copied from Todd and Bowman. Klg. 448.—A circumvallate papilla from the human tongue A, with accessory papillae c, its epithelium a, and nervous. twigs b. B, the ridge running round the papilla, with its nerves b. Copied from Todd and Bowman. ORGANS OF THE BODY. 469 still more so the submucous tissue, is very abundantly supplied with absorbent canals, while the muscular substance is only traversed by regular vessels. In the roots also of the filiform papilke is to be found a capillary netAvork, from which caecal prolongations are sent off into the papillae themselves. The development of the tongue in the embryo commences as early as the sixth Aveek of intrauterine life, in the form of a thick ridge, which seems subsequently to become stationary as regards its groAvth. The papillae are said to be rudimentarily formed in the third month. Remarks.—1. Compare Todd and Bowman, vol. i. p. 437-2. Much variety is to be seen in the form of the filiform papillae. It is not uncommon also to meet with a thread-like fungus, the leptothrix bicccatis, in great quantity among and upon these papillae. §249. Behind the foramen caecum the mucous membrane presents to the unaided eye a more or less smooth appearance. Here the laminated epithelial stratum merely covers a series of small simple papillae, each supplied by a single vascular loop. In this locality a number of different varieties of secreting organs make their appearance. In the first place, even anterior to the foramen caecum, small scattered mucous glands present themselves, Avhich form more posteriorly under the circumvallate papillae, and toAvards the root of the tongue a thick continuous glandular layer. On the under surface of the tongue also, near its tip, are to be found two other racemose glandular masses of considerable magnitude. These empty themselves by several ducts at either side of the fraenum (Blandin, Nuhn). Their functions are, hoAvever, still unknown. From the posterior fourth of the tongue on, finally, the tissue of the mucous membrane, commences to undergo at points a lymphoid metamor- phosis. This may be absent in many mammals, but attains in others, on the other hand, as for instance in the pig, a high degree of develop- ment. In the latter animal this process may advance to the formation of follicles in the larger papillae imbedded in a densely reticulated connec- tive substance (Schmidt). This metamorphosis of the mucous tissue (by which the pharynx also may be affected) leads, as it advances, to the formation of larger and more sharply defined lymphoid organs, varying greatly as regards distribution and structure. They are largely met Avith among the mammals, and are not absent in man. Among these may be numbered the lingual follicles or follicular glands of the mouth, the tonsils, and, at the top of the pharynx, the pharyngeal tonsils, structures discovered some years ago by Koelliker. The lingual follicles (fig. 449) occur in man sometimes scattered, some- times croAvded, upon the posterior portion of the dorsum of the tongue, from the circumvallate papillae doAvn to the root of the epiglottis, and from one tonsil across to the other. They consist of a depression of a greater or less depth (3*5 mm. and upwards), implicating the Avhole of the mucous membrane, so that, beside flattened epithelium, accessory papillae may also exist within the reduplicated portion. Each crypt or depression is enveloped in a thick stratum of reticular connective substance, entangled in Avhich innumerable lymphoid cells are to be found. This stratum extends to immediately beneath the epithelial tunic In it, and distinguished by their looser and wide meshed frame- 470 MANUAL OF HISTOLOGY. work, and consequently lighter shade, a number of small lymphoid follicles may be observed, measuring in diameter from 0*28 to 056 mm. These are sometimes sharply defined, sometimes less distinctly so. Other of these crypts, however, are quite destitute of these follicles. Most usually we find these lingual crypts encased in a strong fibrous capsule. This, however, is also often absent in less distinctly defined examples. a Among and beneath these lingual follicles are generally scattered a great number of racemose glands, whose ducts open partly in the immediate neighbourhood of the crypt (but on the surface of the mucous membrane), and partly Avithin its cavity. In many mammals these lingual follicles are entirely absent, as in the tongue of the rabbit, sheep, and dog. In others they are formed upon the same plan as in man, for instance, in the horse, pig, and ox. Xit" Vi™ S& The blood-vessels and lymphatics are of the same cation of the mucous tis- description as those in the tonsil, to Avhich we sue with its papillae; b, lym- „ , , r ,• phoid portion of the walls refer the reader for minutiae. with several follicles. The tonsUs 0T amygdalce, the largest lymphoid organs of the mouth, are to be found in man and most of the mammalia, presenting, however, considerable variety of structure in the latter. In some of these, moreover, as in the Guinea-pig, the rat, and the mouse, they are entirely absent. The form of the organ, as it appears in the rabbit and hare, is from its simplicity very instructive. Here we find a simple depression surrounded by a thick stratum of lymphoid structures containing small lymph-follicles. The boundary of the organ, externally, is a fibrous capsule. Numerous minute racemose mucous glands lying adjacent, send off their ducts, partly external to the depression, and partly through the lymphoid mass, to empty themselves into the latter. In this case, therefore, these organs sIioav all the characters of a lingual follicle. As a rule, however, the tonsils present a far more complicated structure. They are generally made up of groups of such bodies as those we have just described as representing the tonsils in the hare. These are collected together in greater or less number, their follicular ducts opening either singly on the surface or converging like the corresponding portions of a racemose gland to form passages of greater magnitude. These latter may then discharge their contents, either independently of one another, or, pursuing the same system of confluence, may eventually, as in the tonsil of the ox, give origin to one large excretory duct. BetAveen these two extremes many intermediate forms are met with. Each pit is enveloped in a thick lymphoid layer external to the flattened epithelial lining and mucous membrane papillae often present. This layer, enveloped in dense fibrous tissue, extends as far as the epithelium or its immediate vicinity. As a rule, but not invariably, it contains within a loose tissue a number of follicles. The latter present, both as to number and distinctness of demarcation against the denser interstitial tissue around, considerable variety. Their diameter, in most mammals, is on an average about 0*28 or 0*51 mm. In the dog they may even attain greater magnitude, reaching 0*9-1 *4 mm. The large tonsils of the pig, further, are unusually rich in follicles. Here also are to be met with, as might be expected, numerous racemose mucous glands, playing an important part in the construction of tho ORGANS OF THE BODY. 471 tons Is, and as varied in the arrangement of their excretory ducts as those of the lingual follicles. They discharge their contents, namely, either into the caecal depression of the organ or free on the surface of the tonsil The frequent inflammatory affections to which the amygdalae are subject in adult human beings, render them rather dubious objects of research for which reason specimens obtained from young children should be preferred. Ihe ordinary arrangement of the openings in the adult was found by Schmidt to be either a separate duct for each pit (fig. 450 b) or a collection of the latter to form one large canal (a). The surface' of the organ presented the usual mucous membrane papillae, but the depression only showed traces of them. He frequently encountered, also in the immediate neighbour- c a hood of the tonsils, a few ^^^^^^^^^^i^s^<^^ scattered crypts Avith lym- phoid walls, in which follicles were imbedded, resembling greatly the blind follicles of the tongue (d). This extension, just mentioned, of lymphoid tissue from the fundus of the crypt up to the under surface of the epithelial covering, may be readily seen in the tonsils and lingual follicles of the calf. In some spots even this covering appears not to be completely continuous throughout. Taking this arrangement of parts into con- sideration, it does not seem unwarrantable to suppose that from out the meshes of this superficial reticular tissue, lymph cells may he set free, constituting, when surrounded by the watery secretion of the mouth, those saliva corpuscles so enigmatical as to their origin. This view may be the more safely accepted uoav that we are acquainted with the amoeboid powers of motion of the lymph cells (§ 49). If the mucus welling from the orifices on the tonsils of a newly killed calf be examined, the abundance of saliva cor- puscles to be met with there (Frey) will strike every eye. The blood-vessels (remarkable for the number of highly developed veins among them.) form, with their ramifications, a dense network of coarse and fine tubes, which becomes more delicate as it ap- proaches the surface, Avhere it sends off loops into any papillae which may be present. As soon as follicles commence to make their appearance in this lymphoid layer, the vascular netAvork is restricted to the smaller space of the interfollicular connective-tissue, so that it becomes more dense still. In the follicle itself, however, a very delicate netAvork of radially arranged capillaries is now to be seen, very similar to that already encountered in the follicles of Peyer's patches. 31 Fig. 450.—Tonsil of an adult (after Schmidt), a, large excretory passage; 6, a simple one; c, lymphoid parietal stratum with follicles; d, a lobule strongly resembling a lingual crypt; e, a superficial, /, a deeper mucous gland. Fig. 451.—From the tonsil of the pig. o, depression in the mucous membrane; b, lymphoid tissue; c, follicle; d, lym- phatic vessel 472 MANUAL OF HISTOLOGY. Passing on to the lymphatic canals of the tonsds (fig. 451) (Frey, Th. Schmidt) we find in the neighbourhood of the capsule and in the latter itself, considerable vessels, with valves and knotty dilatations. From these branches are given off, internally, some of which encircle, at considerable distance, the bodies of the racemose mucous glands, and some reach the base and external surface of the different divisions of the tonsils. Here they enter into the formation of a network of canals, Avith greatly ddated nodal points, and some of them penetrate upAvards into the tissue connecting the follicles (b). In the latter situa- tion they are remarkable for their extreme fineness and arrangement in dense but irregular networks. Around the follicles themselves (c), these lymphatic canals form circular networks, their calibre being rather small. The interfollicular lymphatics penetrate, to a greater or less distance, towards the surface of the depression which occupies the axial portion of each division of the tonsil, and end here eventually, blind. The lymphatics of the lingual crypts possess in all salient points the same arrangement as these just mentioned. On account of their near relationship, we will here append a feAv remarks on the lymphoid organs of the pharynx. The latter, in many mammals, is found to present a very extensive lymphoid infiltration of the mucous membrane. In man, the arch of the pharynx is possessed of follicular glands and a pharyngeal tonsil, composed of a number of the latter. This is situated at the point at which the mucous membrane comes into contact with the base of the skull. It is a mass several lines in thickness, which extends from the opening of one Eustachian tube to the other. In structure it resembles the tonsils. The same organ is to be found among the mammalia, as in the pig, sheep, ox, and dog. Other animals, however, are not possessed of it, as, for instance, the hare (Schmidt). According to Koelliker, the first rudiments of the tonsils may be seen in the fourth month of intra-uterine life, in the form of a simple depres- sion in the mucous membrane of the mouth. A month later, several other additional little pits are evident, and the lymphoid infiltrated walls are of considerable thickness. The follicles appear subsequently in the substance of the latter. In the neAv-born child they may be already present, but in many instances this is not the case. The mode of development of the lingual crypts is in its broad outlines the same. § 250. The muscles of the pharynx are made up of striped fibres (§ 164). The tough mucous membrane of the lower portion is covered with simple papillae clothed Avith laminated flattened epithelium. The upper part (fornix), on the other hand, is quite destitute of these, and is covered in the infant with cdiated epithelium, while in the adult body the latter is replaced by the flattened species. This portion of the pharynx, farther, is that most abundantly supplied with glands. These are, in the first place, of the racemose mucous species, and then lymphoid organs men- tioned in the preceding section. The mucous membrane of the pharynx is very vascular, besides being abundantly supplied Avith lymphatic canals. Interlacements of delicate nerve-fibres have also been seen in it (Billroth, Koelliker). We now turn to the oesophagus, which, in its strong external longitu- ORGANS OF THE BODY. 473 dmal layer of muscular fibres, as wed as its fine internal transverse tunic shows a gradual substitution of contractde fibre ceUs for the striped tissue' Jv^fV i iPP?i P^rti°n °f the tube is comPOsed. In the superior third of the latter the first species of muscle alone is to be found Then on the entry of the oesophagus into the thorax, contractile fibre cells begin to make their appearance, either scattered or in groups, first among the transverse bundles, and later, in the longitudinal tunic. After this thev become more and more numerous, so that from about the middle of the tube on the muscle tissue usually appears to be made up entirely of the smooth variety of cells (Welcker and Schweigger-Seidel) remaining so throughout the whole of the digestive tract. The mucous membrane loosely adherent to the muscular tunic beneath is thrown into a multitude of rugae, and contains numerous simple papillae covered by strongly laminated epithelium. In the upper part of the oesophagus large numbers of isolated bundles of vertically arranged con- tractile fibre cells are scattered through it, and lower down a continuous longitudinal Muscularis mucosas presents itself, occupying the deeper Fig. 452.—Oesophageal glands from the human subject. portion of the membrane (Koelliker, Henle, Klein). The latter (at least in the new-born child) is formed of distinct lymphoid tissue (Klein). The glands of the oesophagus (fig. 452 and 453) occurring, it would appear, in varying numbers, sometimes scanty, sometimes abundant, are of the small racemose species, two or three of their excretory ducts frequently joining to form one common canal. At the extreme end of the human oesophagus, about the cardiac opening, are to be found small structures, extending not quite down to the sub- mucosa; these are the cardial glands of Cobelli. Here they form an elevated ring about 2 mm. in height. The blood-vessels are arranged in a moderately loose network of capillaries, and the lymphatics also in a retiform interlacement with small meshes, the tubes measuring about 0*0200 or 0*0699 mm. in diameter, and lying for the most part parallel with the axis of the oesophagus. These latter are situated in the deeper strata of the mucosa, and in the submucous connective-tissue. The arrangement of the nerves here appears to be similar to that in the pharynx. §251. We now come to the description of the stomach (ventriculus), which, on account of the physiological importance of the organ, must necessardy be more minute than that of the last mentioned parts, its mucous mem- brane calling for our special attention. The serous covering of the viscus presents the ordinary structure of Fig. 453.—A small racemose oesophageal gland from the rabbit. 474 MANUAL OF HISTOLOGY. membranes of this kind (p. 226); the muscular substance, consisting of longitudinal, transverse, and oblique fibres, belongs to the involuntary species (§ 163). The mucous membrane of the stomach is clothed from the cardiac orifice on (where the flattened epithelium of the oesophagus terminates Avith an irregular boundary line) Avith columnar epithelium (§ 91), which is continuous from that point on throughout the whole extent of the intes- tinal tube. The ceUs are of the long and narrow species (about 0*6323- 0*6226 mm. in length and 0*0045-0*0056 in breadth). In profile they are seen to possess a cell-membrane, of which the free base of many of them is probably quite destitute during life (Schulze). Younger and smaller epithelial elements may also be seen between the undermost pointed extremities of these cylinders. The surface of the gastric mucous membrane is by no means smooth, but on the contrary very uneven, with prominences varying in height from 0*0751 to 0*1128 and 0*2 mm. The latter possess either a tuft-like form or that of intersecting folds, bounding a multitude of smaller or larger depressions into Avhich the peptic glands discharge their contents. Orifices at the summits of these eminences, on the other hand, never occur. There is much variety, as regards these points, both in different animals and localities. Still more considerable eminences of this kind are to be found at the pyloric end of the stomach, where, as a rule, the mucous membrane attains its greatest thickness, measuring up to 2 mm. iii depth. Towards the cardiac end, on the other hand, where the surface is smoother, the membrane decreases greatly in depth, falling down to from 1*1128 to 0*5640 mm. The proper tissue of the mucous membrane is, owing to the enormous number of glands imbedded in it, but very scanty. As a rule, it pre- sents itself in the form of a soft nucleated connective-tissue of loose texture (fig. 454). It varies, how- ever, considerably in different classes of animals. Beneath the glandular layer is situated a stratum about 0*0564 or 0*1128 mm. in thickness, Fig. 454.—Transverse section through the gas- Consisting of fibrOUS COnnective-tisSUe trie mucous membrane of the rabbit, a, anA intersprtincr musr-lp fiLrea Tn tissue of the mucous membrane; b, transverse " 1Illelbectlng UlUSCie nDreS. in sections of empty and injected blood-vessels; this two lasers may be recognised---an d.openingswherepepticglandsweresituated. interna]j formed principalfy of trang. verse fibres, and an external or longitudinal coat. The relative thickness of these two layers varies greatly in different portions of the stomach (Schwartz). Then from this laminated muscular substance there ascend small bundles of contractde fibre-cells betAveen the glandular follicles. These musculares mucosae, whose beginnings we have already seen in the oesophagus, persist now from this on, with certain variation of arrange- ment as might be supposed, and form integral elements of the digestfve mucous membrane. This constitution, however, of the mucous membrane may give Avay to another. There may appear, namely, between the bands of connective-tissue a greater or smaller number of lymph-corpuscles, pointing to an intermediate form of tissue between that of the gastric ORGANS OF THE BODY. 475 Fig. 455. — Vertical section of the human gastric mucous membrane. a, ridges; b, peptic glands. mucous membrane, and the reticular lymphoid substance of the mucosa ot trie small intestine. The almost innumerable glands of the stomach are of two kinds, not always easy to distinguish from one another, however. These are the peptic and gastric mucous glands. The first of these are those blind tubules, already mentioned in section 198, which are closely crowded together, and occupy the Avhole thickness of the gastric mucous mem- brane in vast numbers (fig. 455, b). The fact that in the neighbourhood of the pylorus in the rabbit about 1894 may be counted upon 1 fj mm. of surface, will give some idea of their abundance. Their length, which corresponds to the depth of the mucosa, is on an average about 1*13 mm., but may fall to the half of this, as well as exceed it by more than double. Their transverse diameter ranges from 0*0564 to 00451 mm. In children the tube is shorter and of smaller calibre. The openings of these tubuli, which may be either grouped together or parted by regular intervals from one another, are roundish orifices considerably decreased in size by the columnar epithelium cells with which they are lined, and which are arranged in a radiating manner (fig. 456). Both chemically and mechanically there may be easily demonstrated a membrana propria on all the tubuli, formed by a condensation of the soft loose connective- tissue of the mucosa in which flat stellate cells have been met with. In the human subject this is only slightly wavy in outline (fig. 457), but in many animals it is on the contrary markedly sacculated, as, for instance, in the dog. The blind end of the tube, which is usually more or less bulbous, is that at which it attains its greatest calibre, while toAvards its opening it is generally somewhat contracted. Double tubuli, although of rare occurrence, may fre- quently be simulated by the crossing of the extremities of adjacent tubuli. Treatment with alkali will generally, however, bring out the true arrangement of parts. Only on very limited portions of the human stomach are deviations from the arrangement of the peptic cells just described to be met with. Thus a very narroAv band of compound tubules is to be found around the cardiac extremity, of which fig. 460, 1, taken from the same region of the dog's stomach, will give an idea. From a common excretory duct of greater or less length (a) 4, 5, 6, or 7 gland tubules spring. Such compound peptic follicles appear to exist in much greater abund- ance among the mammalia As regards the contents of these peptic glands the earlier vieAvs may be summed up as follows. Columnar epithelium lines the depres- sions to a greater or less distance (fig. 460, b). Intermediate ceUular Fig. 456.—Surface of the stom- achal mucous membrane, with scattered openings of the peptic glands, showing also the cylinder epithelium lining the latter. 476 MANUAL OF HISTOLOGY. elements then make their appearance, and after them the specific gland or peptic cells (fig. 457). The form of these when isolated is more or less cubical (fig. 459). They are of considerable size, and almost completely fill the gland tubule. In man they had only been met with in a more or less decomposed Fig. 457. — Three stomach glands from the human being,. partly filled with peptic cells. Fig. 458.—Peptic glands from the human stomach after treat- ment with alkalies. condition (b). In suitable objects (a, c-g) they appear roundish or inde- finitely angular, 0 0323-0*0187 mm. in diameter. They present a delicate boundary layer (e, f, g), or are quite membraneless (a, c), and are com- posed of protoplasm which becomes clear in acetic acid, surrounding a nucleus 0 0074 mm. in diameter, within which a nucleolus may be recognised. Of late years, however, this older view of their nature has been shown to be quite incom- plete. Eecent investigations by Heidenhain and Rollett have adduced much that is new but the extreme difficulty of the subject has prevented definite conclusions being drawn on all points. The conclusions draAvn from our own personal observations are as follows :—The peptic gland consists of several parts ■ with Rollett we distinguish four. Fig. 459. — Different forms of peptic cells from man. ORGANS OF THE BODY. 477 (1.) The first is the entrance portion; sometimes deep, sometimes shadow, in one instance wide, another very narrow. This is the "stomach cell" of English writers, the " Magengriibchen " of the Germans This depression is lined with the ordinary slender columnar epithelium of the surface of the stomach. The nucleus lies far down in the cells and is of elongated oval figure (fig. 461, a). (2.) The second is the undermost portion of the stomach cell, or, if we prefer a term made use of by Rollett, the «inner intermediate portion of the peptic gland." Here (b) the cells, without departing from their Fig. 460.—A compound peptic gland from the dog. a, wide entrance ("stomach cell") lined with columnar epithelium; 6, division; c, the several tubules lined with peptic cells; d, pro- trusion of the contents of the peptic follicle. 2. The opening, a, in the transverse section. 3. Transverse section through the several glands. Fig. 461.—A peptic gland from the cat in side view, a, "stomach cell;" b, inner; c, outer intermediate portion; d, the gland tubule with its two kinds of cells. epithelial character, are broader, lower, and more granular. The nucleus, a round structure, takes up about half the height of the cell. The lumen of this part is usually strikingly narrowed. (3.) The third part now is the "outer intermediate portion" of Rollett (c). It consists of a continuous layer of peptic cells. Exter- nally these are in contact with the membrana propria, and internally they bound the axial canal. We have not been able to find any 478 MANUAL OF HISTOLOGY. other kinds of cells here, although others are stated by Heidenhain to exist. "We are supported in this by Rollett. (4.) Finally, we come upon the true gland tubule (d). Here the picture is entirely changed. The lumen^ is bounded by a continuous layer of a special kind of cell, Avhich in many places comes in contact with the mem- brana propria. External to this layer, and as if imbedded in it, we find our old friends the peptic cells, sometimes few, sometimes in large number. The inner- most cells have been named by Heiden- hain " chief cells," and by Rollett ade- The peptic elements, on the other hand, are spoken of Fig. 462.—Transverse section through the peptic gland of a cat. a, peptic cells; 6, internal cellular elements; c, transverse section of the canillaries. lomorphous cells. Fig. 463.—Peptic glands from the dog, after Heidenhain; the peptic cells darkened with aniline blue. 1. From a fasting animal. 2. A portion swollen up in the first period of iligestion. 3. Transverse and oblique section of the same. 4. Gland fol- licle at the end of the period of digestion. by the first observer as " overlaying cells," and by the latter as " delomorphous" cells. These tAvo kinds of cellular elements in the true peptic gland tube may be easily seen in the dog and cat. Transverse sec- tions also show them (fig. 462). In other mammals also essentially similar relations are likewise to be seen (Heidenhain, Rollett). Heidenhain's observations in regard to the differences to be observed in the ap- pearance of the peptic glands in the states of rest and activity are of great interest further. In a fasting dog (fig. 463, 1) the gland tubules appear shrunken, and usually regu- lar in their outline, while their " adelo- morphous" ceUs are transparent. Some hours after receiving food quite a different appearance presents itself (2, 3). The peptic glands appear swollen, and their walls bulged out at points, the adelomor- phous cells are enlarged and clouded with a finely granular contents. Later on all this swelling up has disappeared (4). The adelomorphous cells are much diminished in volume, but still very rich in granular matter. Which kind of cell now produces the gastric juice, the peptic or adelomorphous 1 or does one species of cell yield the pepsin and the other the acid 1 These questions cannot at present be answered. We are inclined to ascribe the greatest importance to the peptic cells, and with Rollett to regard them as con- tractile elements. ORGANS OF THE BODY. 479 §252. There is beside those just mentioned another species of gastric glands, discovered many years ago in the pig by Wasmann. Here we have tubes with blind endings and hollow down to the latter, which are clothed internally not by peptic cells, but columnar elements like those of epithelium. The tube itself becomes opaque on treatment with acetic acid. These (fig. 464) are the gastric mucous glands (Koelliker). They have since been recog- nised as occurring very Avidely in the stomachs of the mammalia, and may be met with either simple (fig. 464, 1) or compound (2). In the dog, cat, rabbit, and Guinea-pig they are met with near the pylorus in large numbers. They are arranged in a narrow zone in the neighbourhood of the pylorus in man also, but in the form of compound glands (Koelliker). Very accurate observations have lately been made by Ebstein on the stomach of the dog. Here the ordinary columnar epithe- lium of the surface of the stomach is con- tinued down to a considerable depth into the sometimes simple, sometimes compound tube (fig. 465, a). The under portion or blind end presents, on the other hand, lower cellular elements rich in fine granules and clouded (b, b). These resemble in many respects the adelomorphous cells of the peptic glands. They also mani- fest the same differences in the fasting and digesting animal, which were pointed out by Heidenhain (previous §) in the latter. As regards the composition of the tAvo kinds of stomachal gland cells some observations av ere made some years ago by Frerichs. They are composed of an albu- minous substance, and a finely granular matter, pepsin (see below), which may be dissolved out with water. Besides this they contain a certain amount of fats, and among them cholestearin. The ashes, amount- ing to 3-3*5 per cent., consist of earthy phosphates. traces of phosphates of the alkalies, and sulphate of calcium. That their contents have anything to do with the formation of gastric juice has not yet been proved, although some suppose them to have. The existence, in the human stomach, of those ordinary racemose glands which are of such frequent occurrence in most mucous membranes, is denied, and as a rule Avith justice. They are, however, constant in the pylorus, in the form of minute organs imbedded in the mucosa itself. In man they are grouped together in longitudinal bands of from 5 to 7 (Cobelli). Fig. 464.—Stomachal mucous glands. 1. A single gland tube, from the cardial end of the pig's stomach, lined with columnar cells, a, the cells; 6, the axial passage. 1*. isolated cells. 2. A compound gland from the pylorus of the dog. Fig. 465.—From a stom- achal mucous gland of the dog. a, undermost portion of the car.al of exit; b, commencement of the trae gland tube. 480 MANUAL OF HISTOLOGY The lymphoid follicles of the gastric mucous membrane have long been known under the name of the lenticular glands. They are not always to be found in man, but are of rather exceptional occurrence, varying greatly in number, also, wherever they are present. The vascular system of the stomachal mucous membrane (fig. 466), upon which the secretion of the gastric juice and absorption of the fluid con- tents of the stomach is dependent, is very characteristic (§ 197). The arte- ries undergo division immediately on arriving in the submucosa, so that they arrive at the under surface of the true mucous membrane in the form of very fine twigs having an oblique course (figs. 466 and 467, c). Here, with but slightly diminished calibre, they are finally resolved into a delicate network of capillaries (fig. 467, d), whose tubes of 0*0070- 0*0038 mm. are woven around the pep- tic glands forming elongated meshes (figs. 466and 468). Thus they advance as far as the surface of the mucosa, where the orifices of the glands are sur- rounded in a circular mesh-work, and loops are prolonged into any papillae that may be present (fig. 466, above). It is from this last portion of the vascular apparatus alone that the transition of arterial into venous blood takes place. The radicals of the veins are more or less scattered, so that a certain amount of resistance is offered to the flow of blood into them. These venous twigs, then, become very rapidly developed into trunks of considerable calibre, which traverse the mucous membrane per- pendicularly downAvards to empty themselves eventually into a wide- meshed network lying horizontally underneath the latter (figs. 466 and 467, b, a). This arrangement per- sists, as a rule, throughout the vari- ous species of mammals, with slight modifications, affecting principally the surface of the mucous membrane. In the long-meshed network of capillaries we have before us that portion of the vascular system pre- siding over the secretion of the organ, and in the round meshed network with the venous radicals, that part formerly erroneously supposed to be devoted to absorption. Fig. 466. — Vascular network of the human gastric mucous membrane (half diagramma- tic). A fine arterial twig breaks up into a long-meshed capillary network, which passes again into a round-meshed around the open- ings of the glands. From this latter the vein (tlie large dark vessel) takes its origin. Fig. 467.—From the stomach of the dog. a, a vein; 6, its branches; c, an arterial twig break- ing up into a capillary network (d) for the peptic glands. ORGANS OF THE BODY. 481 As regards the lymphatics of the stomach, only the deeper were knoAvn until quite recently. According to Teichmann — with Avhose views my own observations are in perfect harmony—there exists be- neath the peptic glands a network of lymphatic canals, about 0*0305-0*0501 mm. in diameter, which communicate with a deeper -wide meshed netAvork of passages of larger calibre, measuring transversely, from 0*1805 to 0*2030! From these latter the true, valved lymphatic vessels are then developed, which gradually perforate the muscular tunic to follow subsequently the tAvo curvatures of the stomach. For many years this was supposed to be the true arrangement of parts, and numerous efforts were made to prove that the superficial veins of the stomachal mucous membrane presided over the absorption of the organ. Fig. 468.—Undermost half of peptic glands from the dog, with their long meshed capillary networks. Fig 469 —Lymphatic vessels in a vertical section of the mucous membrane of the stomach of an adult man (original drawing by Loven). But quite recently this difficulty has been got over at the hands of an excellent Swedish observer, Loven, whose dexterity we may thank for the injection of these passages, and that of the highly developed lym- phatic apparatus, whose radicals ascend almost to the surface of the mucous membrane. The arrangement of these will be easily understood from fig. 469, and no further explanation need be given. The nerves of the stomach, derived from the vagus and sympathetic, are arranged in the submucous tissue in a plexus studded with numerous minute ganglia (Remak, Meissner). The greatest obscurity, however, still remains as to the ultimate termination of the fibres. 482 MANUAL OF HISTOLOGY. The development of the stomach is a subject in the history of develop- ment to which great interest attaches. We will, however, occupy our- selves only with its accessory organs. These, the tubular glands, commence in the form of pointed processes, springing downwards from the intestinal glandular germinal plate, which become gradually hollow, beginning at the openings. It is a point worthy of notice, that these glands are for a long time entirely unconnected with the subjacent loose fibrous intestinal layer°; and it is not until the fifth month of intrauterine life that the latter' sends up tufted processes between, the gastric tubuli to form the mucosa of the part (Koelliker). §253. The mucous membrane of the non-functioning stomach is pale in colour, and more or less completely covered by a quantity of either slightly acid or alkaline slimy mattter of considerable viscidity. This is the secretion elaborated by the gastric mucous glands. In it may be seen, under the microscope, beside cast-off columnar epithelium, numerous peptic cells escaped from the peptic tubuli, and frequently, also, a number of more or less broken down structures of the same nature, naked cells, and free nuclei surrounded by particles of the original cell contents. According to Briicke and Bernard, it is only the surface of the mucosa which is acid in the living animal, the deeper portions having an alkaline reaction. After death the whole becomes rapidly acid owing to diffusion. On the introduction of food into the stomach, or under the influence of other chemical or mechanical excitants of the gastric mucous mem- brane, the condition of things is immediately changed. Owing, probably, to some reflex action not yet understood, although indicated in many ways, an increased influx of blood into the intricate vascular interlacements of the mucosa takes place. The veins become distended, and contain brighter blood, and the whole surface appears to the unaided eye of a more or less rose-red colour, in addition to which phenomena the temperature rises. Coincident with these changes the gastric juice commences to Avell up from the tubules, bearing with it numerous peptic cells from the lining of the latter. This juice is a transparent fluid of strongly acid reaction, either perfectly colourless or of a pale straw tint. It takes up certain constituents of the mucous coating of the stomach, and extracts subsequently various fer- menting substances from the granular contents of the peptic cells, a process which commences whde the juice is still within the tubuli in Avhich the peptic cells are contained. It is likewise mixed Avith whatever saliva may have been SAvalloAved. It cannot then be a matter of surprise that the gastric juice possesses a specific gravity of T001, 1*005, and 1*010. The proportion of solid constituents in this secretion is, as a rule, small but variable. Thus, in the sheep, it contains, according to Bidder and Schmidt, T385, and in the dog, 2*690 per cent., while, according to the last named observer, that of the human female only contains 0*559 per cent. The nature of the fluid also would lead us to expect consider- able variety also in one and the same individual. The tAvo most important of these constituents are a free acid and peculiar fermenting substance, Avhich possesses in the presence of the former, and only then, a great amount of energy. The acid in question has given rise to much debate regardincr its ORGANS OF THE BODY. 483 nature. It has been held at different times to be either lactic or hydro- chloric, Avithout taking into account a number of other ill-founded theories. The matter has been at last set at rest, however, by C. Schmidt in favour of the latter vieAv. Lactic, acetic, and butyric acids may! hoAvever, be present as decomposition products, the first being indeed a very frequent constituent of gastric juice. 0 02 per cent, of hydro- chloric acid was discovered by Schmidt in the gastric juice of a female, and 0*305 per cent, by Bidder in that of the dog. The ferment found in the gastric juice is known as pepsin. It was many years ago made the object of very extended investigation by Schwann and Wasman, and since then by many other observers, but can hardly be said to have ever been obtained completely pure. Its propor- tion generally amounts to about, on an average, 1 per cent. Bidder and Schmidt's analyses give 1*75 for the dog. 0*42 for the sheep, and for man only 0*319 per cent. At present but little is known of pepsin as about all the other fermenting substances of the animal economy. We are aware, indeed, that it occurs in a soluble form, is precipitated by alcohol Avithout losing its digestive power on subsequent re-solution in water, whilst elevation of temperature above 60° C. destroys this for ever. This pepsin, as has been shown by Frerichs, is the granular matter seen in the contents of the peptic glands. It appears to possess almost unlimited digestive properties in the presence of an adequate amount of dilute acid, so that there seems to be an inexhaustible store of it in the mucous membrane of the stomach. The mineral constituents of the gastric juice are, chlorides of the alkalies, phosphatic earths, and phosphate of iron (Bidder and Schmidt). Among the first we find a great preponderance of common salt, and besides chlorides of potassium, of calcium, and of ammonium also. We shall take an analysis by the two last named observers as an example of the proportions of the various salts. The percentage in the gastric juice of the dog was as folloAvs : Chloride of sodium, 0*251; of calcium, 0*062; of potassium, 0*113; of ammonium, 0*047; phosphate of magnesium, 0*023; of calcium, 0*173; of iron, 0*008. Just as the peptic cell is able to produce pepsin from an albuminous substance, so also does it yield hydrochloric acid by the splitting up possibly of the chlorides. This process, however, is probably carried on only at the undermost portion of the gland tubule, i.e., near the orifice (Briicke), the source of the watery fluid with its salts being the long- meshed capdlary network of the peptic glands. The amount of gastric juice poured out is naturally very variable, owing to the periodical * nature of the functions of the stomach, and therefore necessarily difficult to determine. It is stated by Bidder and Schmidt to be at all events very considerable. A dog of about a kdogramme weight produces, in the course of a day, about 100 grammes, with extremes in both directions. Schmidt estimated the amount secreted hourly in the body of a woman at the enormously high figure of 580 grammes. The use of this fluid is to dissolve the albuminous matters taken into the stomach, and to convert them into peptones, i.e., modifications of these substances which neither coagulate at boiling point or under the action of mineral acids, nor combine with metallic salts to form insoluble compounds (Lehmann). They transude, on the other hand, with great readiness through animal membranes, a property of the utmost import- 484 MANUAL OF HISTOLOGY. ance, which undigested albumen does not possess. In contradistinction to the latter, then, these peptones might be designated as albuminates capable of being absorbed. Owing, however, to the extreme difficulty of the subject, there still exists up to this very hour a great difference of opinion among physiologists as to the nature of peptone, in spite of the exertions of very excellent observers (Briicke, Meissner). § 254. The small intestine, with its serosa and Avell-known double layer of muscle fibres, presents, as regards its mucous membrane, a far more Fiff. 470.—From the small intestine of the vab- Fig. 471.—Vertical section of the mucous mem- bit. a, tissue of the mucous membrane; 6, brane of the small intestine of a cat o, the lymphatic canal; c, an empty transverse sec- glands of Lieberkuhn; b. villi. tion of a gland of Lieberkuhn; d, another of the same occupied by cells. complicated structure than that of the stomach. This membrane, in the first place, is thrown out into a multitude of crescentic duplicatures, known as valvules conniventes Kerkringii, and is covered in the next by innumerable small conical processes, the villi intestinales. By this arrangement of valves and tufts, an enormous increase of surface is obtained. We find, further, in the tissue of the mucosa, two forms of glands, namely, the racemose mucous glands of Brunner, and the tubular of Lieberkuhn, to which may be added the lymphoid follicles, either single or in groups, knoAvn as the solitary and agminated glands of Peyer. But the tissue of the mucous membrane itself (fig. 470), is also different m texture from that of the stomach. Thinner, and supplied with the muscularis mucosas, it no longer presents the character of ordinary fibrous tissue, as does that of the stomach as a rule. It consists rather of reticular connective-tissue, containing, entangled in its interstices and meshes, an abundance of lymphoid cells, and only assuming a more 01 less homogeneous membranous structure towards the gland cavities and towards its free surface, whilst at other points, as, for instance, near the surface of large vessels, it appears to be made up of longitudinal fibres This tissue of the mucous membrane varies also to a certain extent according to the different species of animals. The villi commence on the intestinal aspect of the pylorus flat and Ioav at first, and increasing gradually in height until they assume a conical or pyramidal form, which merges step by step, as we prom-ess downwards, into a slender tongue-like figure. They stand tightly packed ORGANS OF THE BODY. 485 one against the other (fig. 471, 6), so that, according to Krause's estimate, about from 50 to 90 spring from 1 Q mm. in the jejunum, and duodenum, and in the deum from 40 to 70, oivino* for the whole extent of the small intestine, accord- ing to his calculation, 4,000,000. Their height varies from 0*23 to IT3 mm. and upwards. Their breadth also differs, naturally, according to their form. Transverse sections show them to be either cylindrical or leaf-shaped. All these villi are clothed wdth peculiar col- umnar epithelial cells, already referred to (p. 147), which present on their free surfaces a thickened border, perforated by pores or fine canaliculi (fie 472, a). Between these cells (fig. 473, b) may be ob- served—not unfrequently distributed with toler- able regularity—those "goblet cells" Avhich have been already brought before our notice (§ 93). In number they vary with the species and the individual. We also encounter here, as in the stomach, small roundish structures lying between the in- ternal extremities of the columnar epithelium cells. These may be regarded as destined to replace the latter as they successively perish. Under the epithelial layer we next come upon the framework of the structure in the form of reticular connective - substance with entangled lymphoid corpuscles and nuclei in some of the nodal points of its not unfrequently long meshed network. The recognition of the true nature of the surface of the villus is attended with considerable difficulty. Nevertheless, we may see that here also it preserves the same retiform character, although the bands may in many instances become broader and flatter, and the interspaces between them decrease in size until they become merely small apertures, so that the effect almost of a homogeneous mem- branous limiting layer may be given. This tissue of the villi is traversed in the first place by a vascular network (b), next by a lymphatic canal (d), occupying the axis of the structure, and lastly, by delicate longitudinal bundles of unstriped muscular fibres (c). For the discovery of the latter we are indebted to Briicke, although anterior to his researches on the subject, distinct contractility had been recognised in the intestinal villi in the living or recently kdled animal, producing numerous wrinkles on the surface of the process (Lacauchie, Gruby, and Delafond). These bundles of muscle fibres may be traced down through the mucous mem- brane into the muscularis of the latter. The vascular networks of the intestinal villi (figs. 474, 475) occupy invariably the peripheral portions of the latter, and are supplied in the smaller mammalia each by a small arterial tAvig or pair of the same (a), Fig.472.—An intestinal villus (after Ley dig), a, columnar epithelium with thickened border or cuticular mem- brane; b, capillary network; c, longitudinal muscular bundles; d, axial chyle radicle. Fig. 473.—Epithelial cells from a human intestinal villus (after Schulze). a, goblet cells; b, ordinary elements. 486 MANUAL OF HISTOLOGY. Fig. 474.—Vascular system of an intestinal villus in the rabbit, a, the arteries (shaded), breaking up first into a capiilary network around the glands of Lieber- kuhn (d); b, network of capillaries in the villus; c, venous vessels (unshaded). which ascend at one side, bend over at the apex, and follow the opposite wall in returning, as venous vessels (c). Between these afferent and efferent vessels a capillary net- work exists, sometimes exceed- ingly complex, sometimes very simple in its arrangement (b). It not unfrequently happens that a system of capillaries is first given off by the arterial twig to supply the glands of Lieberkuhn (d), opening at the base (fig. 474, a to the right) of the villus, which system is simply continuous with that of the latter (b to the right). The diameter of the arterial vessel may rise to 0*226-0*0282 mm., that of the vein to 0*0451 mm. In calibre the capillaries measure on an average 0 0074 mm., and their arrangement is usually in elongated meshes. The disposal in loops of the arteries in their transition into veins may be absent, a capillary network being interposed betAveen the two vessels at the summit of the villus. We have already alluded (p. 374) to the ccecal chyle canal of the intestinal villus. When the latter is more than usually broad there may be two or even several of these blind tubes, but Avhen small and slender they are only single. The chyle canal occu- pies the axis of the villus, and presents itself, under ordinary treatment (fig. 472, d), in cer- tain cases quite distinctly as a tube formed of a homogeneous non-nucleated membrane, on an average 0*023 mm. in diameter. On treatment with a solution of nitrate of silver, however, this tube is easily shoAvn to be composed of a layer of those jagged-edged vascular cells already so frequently alluded to. It may be seen with great clearness when injected artificially, and also in the villi of animals killed while engaged in digesting an abundance of fatty food (fig. 476). §255. Turning now to the glandular elements of the small intestine, we shall commence with the least important, namely, with the race- mose mucous glands (fig. 477, b), known com- monly as Brunner's. They are confined to the duodenum, and begin close to the stomach, closely crowded together into a regular adenous layer Fig. 475.—Vascular network from the intestinal villus of a hare, with its arterial branch 6, capillaries c, and venous branch a. ORGANS OF THE BODY. 487 seated immediately under the mucosa. Thus they extend as far as the orifice of the ductus choledochus, and from that point on appear more rarely. Among the mammalia much variety is observed as regards tiitae organs. When only slightly developed, as is frequently the case, they are confined to the neighbourhood of the pylorus, forming a complete zone just behind it. The diameter of these glands ranges from 0*23 to 2 mm. The branches of the excretory ducts present a complicated series of twists unlike other glands of the same kind (Schwalbe). The acini are round, elongated, or even tubular, and measure from 0*0564 to 0*1421 mm. The ex- cretory canals of these glands, con- siderable in calibre (fig. 477), ascend obliquely upwards, slightly bent, dis- charging their contents at the base of the villi (fig. 477, c). Both excretory duct and gland vesicle are, strange to say, lined by the same species of cells. These are low columnar elements, whose nucleus is situated low doAvn in the body, and which are but very slightly coloured by carmine. They are unlike the contents of the follicles of Lieberkuhn soon to be described. Fig. 476.—Very slender villus from the intestine of a kid, killed while engaged in digestion; without epithelium, and showing the absorb- ent vessel in the centre filled with chyle. a- c Fig. in.—Brunner's glands from the duodenum, a, villi; 6, bodies of glands; e, excretory canals opening between the villi. That same network of extremely delicate gland canaliculi we have already spoken of as occurring in many racemose organs (§ 195), as well as in the salivary glands (§ 245), is to be found also in the glands of Brnnner, according to Schwalbe. The membrana propria, which is here 32 488 MANUAL OF HISTOLOGY. completely closed, and contains imbedded nuclei, sends no processes into the interior of the gland vesicles. Fig. 478.—One of Brunner's glands from the human being. These organs appear to be richly supplied with lymphatic vessels of large size, which penetrate between their vesicles and lobules. The secretion of these glands appears to be peculiar. According to Schwalbe, the contents manifest considerable similarity to those of the stomachal mucous glands already alluded to (§ 251). Heidenhain tells us that in the dog, at least, the cellular elements of Brunner's glands present the same changes in the fasting and digesting condition that were observed by Ebslein, in those of the stomachal mucous membrane. According to Budge and Krolow, the contents of these organs convert (in the pig) starch into dextrin and grape sugar, and dissolve fibrin at 35° C, but have no effect, on the other hand, on either coagulated albumen or fat. In the dog and horse the secretion is rather viscid, and contains a considerable amount of mucus (Costa). The crypts of LieLerkiihn, on the other hand, are glands of far greater importance. They are to a certain extent a modified extension of the mucous glands, as they are called, of the stomach. The whole of the mucous membrane of the small intestine, bike that of the stomach, is beset Avith an enormous number of these crypts crowded closely together perpendicular to the surface of the membrane (fig. 479). The arrangement of their vascular supply is similar to that of the peptic glands. The length of these crypts is less than that of the gastric tubuli, ranging from 0*3767 to 0*4512 mm., with a breadth of 0*0564-0*0902 • mm. Their membrana propria is hardly distinguishable from the surrounding connective-tissue. It is delicate, and the outline of the tube is conse- quently smooth. At its blind end we may either find a dilatation or decrease in calibre. Fig. 479.—Lieberkiihn's glands from the cat, with broken down cellular contents. ORGANS OF THE BODY. 489 The contents of these crypts unlike those of Brunner's glands, consist of delicate columnar nucleated cells, with Avidened base, which rest on the membrana propria. These, together with the open axial canal, may be seen in every transverse section. (fig. 470 d). According to Schulze, between these cells other goblet cells may present themselves, a point worthy of note. In suitable preparations (fig. 480) the orifices of the glands are to be seen at varying dis- tances from one another, lined with columnar epithelium, which passes in through the en- trance of the tube. At those points at which the villi are very crowded, the orifices of these glands of Liebekiihn surround their bases in rin^s. Fig. 480.—Openings of the glands of Lieberkuhn inthemouse. At (a) an empty opening, in the other cases each is filled with columnar cells, placed with their long axis towards the centre. 256. Fig. 481.- One of Peyer's glands from the rabbit. We now turn, finally, to the lymphoid follicles of the small intestine. These occur with greater frequency here than in the stomach, which fact is explained by the greater similarity of their tissue to that of the mucosa of the small in- testine. As has been already mentioned, they are in the first place met with scattered over the whole length of the small intestine as glandulai solitarias. These are roundish, opaque, white bodies of very unequal size, ranging from 0*2 to 0*4 and 2*2 mm. In some subjects they are very scantily repre- sented, or even entirely absent, Avhile in other cases they appear in mul- titudes. In situation and structure they correspond with the agminated glands into Avhich they may merge without any sharp boundary. At parts of their periphery they are continuous with tl e circumjacent connective- tissue. By the agmination of these follicles it is that Peyer's patches or plaques are formed (figs. 481, 482), which occur in man, as in all mammalia, in the greatest abundance, but in very various degrees of develop- ment. In some cases they are made up of from 3 to 7 follicles only, but more fre- quently of from 20 to 30. Again, Avhen large, they may contain up to 50 or 60 of the latter. Peyer's patches are found principally in the small intestines, and ahvays at the free side, or that opposite to the mesenteric attachment of the viscus. They appear, as a rule, first at the end of the jejunum, and become more frequent in the ileum. But although this is the usual mode of .distribution, it is not without Fig. 482.—Vertical section through one of Peyer's glands from the rabbit, a, villi; 6, bodies of glands rounded off above; c, others, apparently open above. 490 MANUAL OF HISTOLOGY. exceptions, especially in the occurrence of isolated Peyer's glands in the colon. The vermiform appendix of man, and to a greater extent also that of the rabbit, may likewise be said to be one large Peyer's gland, composed of crowded follicles (Teichmann, His, Frey). The number of these agminated glands to be found in the human small intestine varies from 15 to 50 and upwards. The diameter of such a group cannot, of course, be definitely laid down, varying, as it does, from 7 mm. to several centimetres. The form they assume is usually oval, their long axis corresponding with that of the intestine. Subjecting the glandulce agminatce to close inspection, we find in longitudinal sections that, although the form of the follicles may be similar in one and the same group, nevertheless it is liable to vary to a large extent, both in different animals, and according to the locality in the intestine we choose for examination. Beside spheroidal follicles, namely (fig. 483), we meet Avith others more or less elongated, presenting somewhat the figure of straAvberries. But in other instances the follicles may be so increased in vertical diameter as to present on section an outline resembling that of the sole of a shoe. In Fig. 483.—Vertical section of one of Peyer's plaques from man, injected through its lymphatic canals a, villi, with their chyle passages; 6. follicles of Lieberkuhn; c, muscularis of the mucous membrane • d, cupola or apex of follicles; e, mesial zone of follicles; /, base of follicles; g, points of exit of the chyle passages from the villi, and entrance into the true mucous membrane; h, retiform arrange- ment of the lymphatics in the mesial zone; i, course of the latter at the base of the follicles- k confluence of the lymphatics opening into the vessels of the submucous tissue; ;, follicular tissue of man they are usually of the spheroidal kind ; in the small intestine of the rabbit strawberry shaped. Those very much elongated examples just mentioned are to be found chiefly in the under portion of the ileum of the ox and vermiform appendix of the rabbit. The follicle, however, may be of what shape it will, Ave can always distinguish three portions in it, namely, the summit or cupola, the mesial zone, and the base. The cupola (d) projects into the intestinal tube * the base (/) descends to a greater or less depth into the submucous connective-tissue; and the mesial zone (e) serves to connect together all ORGANS OF THE BODY. 491 These Fig. 484.—From the surface of the pro- cessus vermiformis of the rabbit, a, narrowed entry to the cupola of a fol- licle ; 6, mouths of crypts in the broad ridge of mucous membrane; c, hori- zontal lymphatic network; d, descend- ing lymph canals. the follicles of one gland by means of a tissue entirely simdar to their own. It is also continuous, without any line of demarcation, with the adjacent infiltrated retiform tissue. It is at its level that Ave usually find the muscularis mucosas (c) Avhich opens in each case to allow room for the follicles (Frey). We must noAv turn to the nearer consideration of the cupohe. are surrounded by annular ridges of mu- cous membrane, containing follicles of Lie- berkuhn (b), and are continuous down- wards into the mesial zones, supporting on their free surface, either ordinary or, what is more frequently the case, someAvhat modified irregular villi (a). The actual summits of the follicles, hoAvever, are quite destitute of villi. They are, in fact, so freely exposed that each lymph follicle appears to the naked eye as a little pit on the surface of the plaque. The ridges around the follicles may, hoAvever, as in the plaques of the colon, be quite bare of villi. In the processus vermiformis of the rabbit, also, the surfaces of the rings may be increased greatly in breadth (fig. 484, 6), so that only a narroAv entrance (a) to the follicles is left. If we turn now to the finer structure of the elements of Peyer's patches, we find it to be exactly that of other lymphoid follicles. Their sustenta- cular tissue is a species of retiform connective sub- stance, traversed by capil- laries in Avhich innumer- able lymph cells are entangled (pp. 195 and 420). Many of the nodal points in this network contain in young indivi- duals full-bodied nuclei, met with in adults, on the other hand, in a shrunken condition. At the mesial zone this reticular tissue is continuous Avith the similarly constituted connecting lymphoid layer, and through this with the closely related tissue of the mucous membrane. The sustentacular matter in the interior of the follicles is very loosely interwoven, Avhile externally it assumes a denser texture. At two spots it becomes exceedingly densely reticulated and distinct; in the first place on the surface of the cupola, which is, like the viUi, covered immediately by columnar epithelium, and then at the peripheral portion of the base. This latter in some of Peyer's glands is surrounded by a continuous investing space, which corresponds to the investing spaces of the lymphatic glands (§ 223). In many animals the resem- blance is increased by the interposition of perpendicular fibrous septa Fig 485.—Vertical section through an injected Peyer's follicle of the rabbit, showing the capillary network of the same; the large lateral vessels, 6, and those of the villi, c. 492 MANUAL OF HISTOLOGY. betAveen adjacent investing spaces, which are lost at the level of the mesial zone. In other plaques, instead of these continuous investing spaces, the surface of the base is covered by numerous fine lymphatic canals, like a chdd's toy ball with a net. .* In the connecting layer, between the mesial zones, a network of similar passages may likewise be recog- nised. The walls of these pas- sages, then, are made up of very small-meshed lym- phoid reticular substance. In the actual follicles themselves, however, no such passages exist. We have only to add, that the superficial lymphatic canals of the mucous mem- brane, of the smooth as well as villous annular ridges, all sink down to empty themselves into these lymph passages of the con- necting layer aheady men- tioned ; also that, at least, a part of the investing spaces around the follicles is clothed with the characteristic vascular epithelium of the lymphatic system (p. 377). J l The vascular supply of each follicle is composed (as was demonstrated many years ago by myself) of an exceedingly complex network of delicate capillaries, irom about 0*0056 to 0*0074 mm. in diameter. This network (hg. 485 a) stands m close connection with the large arterial and venous vessels (b) which course up and down between the follicles supplying the villi (e) of the intestine, as may be seen in vertical sections. In trans- verse sections the arrangement of the capillaries in the interior of the foUicles is seen to be in lines converging towards the centre (a), starting from circular vessels externally-an object of extreme beauty under the microscope. J §257. The nervous apparatus of the small intestine is exceedingly compli- cated denying its roots from the ventral divisions of the vLus and sympathetic. It consists of a double plexus of microscopic gangha con nected above with the nerves interlacing in the walls of the stomach In the submucosa we first meet with the plexus of Remak and Meissner remarkable for its highly developed knots. From this pal, nudTted fibres are given off, principally to the muscularis of the mucous mem brane, and muscular bundles in the villi, and to a minor extent to the surface of the membrane as sensory elements. We are still lack4^ observations on these points, hoAvever. tacking in Fig. 486.—Transverse section through the equatorial plane of three of Peyer's follicles from the rabbit, a, capillary net- work ; b, large circular vessels. ORGANS OF THE BODY. 493 Externally this submucous plexus is connected Avith the remarkable and no less developed plexus myentericus of Auerbach. The latter, with its regularly flattened ramifications, but more minute ganglia, is situated between the internal transverse and external longitudinal muscular tunic of the gut. These it supplies with its numerous twigs, forming first a secondary plexus of threads, 0*001- 0*005 mm. in thickness, each of which possesses from 3 to 6 of the finest nervous filaments (L. Gerlach), leav- ing no doubt as to the motor nature of the latter, although we are still in the dark as to the ultimate termination of the fibres. We may form some esti- mate of the extent to which the nervous system of the in- testines is developed, from the fact that about 100 ganglia, belonging to the submucous, and over 2000 to the myen- teric plexus, are to be found in 1 □'/ of the intestine of the rabbit. The following is the general arrangement of the vessels of the intestine. On arriving in the wads of the latter, a few small twigs are given off Fig. 487.—A ganglion from the submucous tissue of a human infant, a, nervous knot; b, radiating twigs; c, capillary network. Fig. 488. -From the small intestine ofthe Guinea-pig. a plexus myentericus, with its ganglia; b, c, fine, and d, larger lymphatic vessels. to the serous covering of the part, after which the vessels break up in the muscular tunics into the usual well-known capillary network with elongated 494 MANUAL OF HISTOLOGY. meshes, whose long axes correspond with that of the contractile elements. The submucosa is from tins supplied further with another network of capillary tubes of somewhat greater calibre than the first (Frey). The chief supply, however, is to the mucous membrane itself. Here arterial twigs arriving at the bases of the crypts of Lieberkuhn gradually break up into networks of capillaries of medium calibre, with oblong meshes, similar to those of the peptic glands. These are disposed, in the first place, around the mouths of the glands in delicate rings, and then continued into the mesh-work of the villi. The veins arising in the latter, with which we are already acquainted, descend directly downwards through the mucous membrane, receiving but few lateral twigs, and empty themselves into the submucous venous network. The. presence of racemose glands and lymphoid follicles necessitates, in many parts of the intestinal tract, a modification of this vascular arrange- ment. The well-known round-meshed network, for instance, is met with around Brunner's glands in the duodenum. Then Peyer's patches require a more highly developed vascular system. Here little arteries ascend, either in the septa, or the connecting or junction layer of the follicles, after sending off twigs for the fundus of each of the latter, as well as for their sides. Thus they reach and break up into the terminal capillary network of the ridges and intestinal villi. From thence the blood is taken up by lateral branches of the veins arising here, which descend by the side of the arteries, receiving also an addition from the follicles. § 258. Through the exertions of Teichmann, His, Frey, and Auerbach, Ave have recently become accurately acquainted with the nature of the lymphatic apparatus of the small intestine. This is from many points of view of great interest. Its roots have two sources: in the first place, the mucous membrane with its villi, and then the muscular coats of the intestine. The last source was only lately discovered by Auerbach, while the first has long been known, owing to the fact of the vessels here being so distinctly visible Avhen full of chyle. A few hours after the reception of fatty food into the stomach, the matters found in the small intestine are found to contain neutral fats in a condition of the most minute division, a physical change brought about by the admixture with them of the bile and secretions of the pancreas and mucous membrane of the intestinal tubes. The fats are now in a condition capable of being absorbed, and they are soon taken up in large quantities. In this last process the villi are especially active, if not exclusively so, and principally their apices. The commencement of the process is as follows : The fatty "lobules in the form of extremely minute particles of from 0*0045 to 0*0011 mm in diameter, after passing through the thickened porous border on the epithelial cells, arrive within the bodies of the latter. At first only a few cells are seen to be filled in this manner, the fatty granules occupy- ing principally that portion of the ceU between the nucleus and the free end. The number of cells, however, presenting this fatty infiltration soon becomes greater and greater, and the fat-molecules penetrate past the nucleus into the pointed and attached half of the columnar elements In the further progress of this process the granules of fat pass throucdi the apices of the cells into the tissue of the mucous membrane beneath ORGANS OF THE BODY. 495 either filling the whole apex of the vdlus in such myriads as to give it the appearance of being diffusely infiltrated, or else ranging themselves in long streaks which may be mistaken for fine canals charged with fatty globules as they course along between the lymph cells and connective- tissue fibres. In the third stage of the process we remark that the minute fatty molecules have penetrated through the walls of the chyle radical mto its lumen, entirely filling the latter, so that this element of the intestinal villus, at other times so difficult of detection, becomes dis- tinctly- visible, as has been already mentioned. The concluding phase of he whole act is especially instructive; here we see the columnar epithe- lial cells and tissue of the mucous membrane again freed of fat, while the chyle vessel is stdl full (fig. 476, p. 487). That this is the true course of the process may be confirmed by artificial injection of the lymphatic canals in the mucous membrane of the small intestine. The radicles of the chyle or lacteal system (fig. 489) are easily recog- nised in the villi of the gut as blind canals, which in our opinion (in Avhich we are supported by Teichmann and His), are not continuous with the actual tissue of the villus. According to the form of the latter thev present themselves either single (a) or double (b), or even in greater number (e). In the last case we either find a looped communication between them in the apices of the villi, or the vessels end separately toAvards the roots of the villi we not unfrequently encounter transverse connecting branches. On arriving in the mucous membrane after leaving the villi, the lacteal vessels descend through the former between the follicles of Lieberlmhn, either directly or subsequent to the formation of a superficial horizontal F"ig. 489.—Vertical section of the human ileum, a, villus, with one chyle canal; b, another with two; c, another with three; d, absorbent canals in the mucous membrane. network, which lies at the bases of the villi, and encircles with its meshes the mouths of these glands of Lieberkuhn. At the boundary between the mucosa and submucosa, and in the latter, a network (d) is formed by the intercommunication of these chyle canals. These latter may be of considerable calibre, as in the sheep and rabbit, or small, as in man and the calf. They accompany the network of blood-vessels also here, and in some cases form sheaths around the latter. As a Avhole, moreover, much variety is met with among them, depending on the thickness of the mucous membrane and species of animal chosen for observation. 496 MANUAL OF HISTOLOGY. The arrangement of the lacteals is modified wherever Peyer's plaques occur (fig. 490). Those lymphatic passages (a), returning from the modified villi of the circular ridges of these localities, form around the tubular glands (b) of the villous ridges a netAvork (g), which is continuous with another system of intercommunicating passages (h) formed in the reticular substance encircling the mesial zones of the follicles. The latter open either into simple investing spaces enveloping the basal portions of the follicles, and precisely similar to those of the follicles in a lymph gland (in the rabbit, sheep, and calf for instance), or (the case in man, the dog, and cat) these spaces are replaced by a system of separate canals (i), interlacing around the bases of the follicles like those we have already considered in § 227. From this set of passages, or from the simple investing space, as the case may be, the efferent lymph vessels finally take their rise. Returning now to the system of canals of the submucous tissue, we Fig. 490. find springing from it a certain number of regular knotted lymphatic vessels, which empty themselves, after piercing the walls of the intestine, into the subserous lymphatic trunks. These latter are arranged in a narrow band following the mesenteric attachment of the gut (Auerbach). The submucous lacteal network communicates, moreover, by means of another set of passages with a second plexus of lymphatic vessels lying betAveen the longitudinal and transverse layers of muscle of the part. This (fig. 488, p. 493), to which the name interlaminar network has been given by Auerbach, accompanies the plexus myentericus situated here also, with which we are already acquainted. It collects all the lymph from the muscular substance of the intestinal tube, from a series of very densely reticulated lymph canals of exceedingly small calibre, which are found singly in the longitudinal tunic, but bedded one over the other in the transverse layer. This interlaminar lymph net is connected finally Avith the subserous trunks by efferent vessels. In this complex arrangement there is most undoubtedly a double pro- ORGANS OF THE BODY. 497 vision made for the escape ot the chyle, as Auerbach very correctly remarks, and during the peristaltic action of the bowel, also, the latter fluid is able on this account to give way to the pressure in many directions. In conclusion, Ave have only to state, as regards the development of the small intestine, that in man the villi make their appearance in the third month of intra-uterine life. They are then apparent as wart-like excres- cences. Further, we would point to the fact, that the crypts of Lieberkuhn, unlike the gastric tubuli, are present from the commencement as pits in ' the mucosa, and that the follicular structure of Peyer's glands is apparent in the seventh mouth. The cells of the intestinal mucous membrane, and of Liebe'rkiihn's follicles, contain glycogen in the foetus (Rouget). § 259. The mucous membrane of the colon corresponds in most essential particulars with that of the small boAvel, except that it is quite destitute Fig. 491. — Tubular glands from the Fig. 492.—Tubular gland from the colon of a Guinea- rabbit's colon. One tube filled with pig. At a, a tube is seen with membrana propria cells, the others sketched without apparent at certain points; at 6, the contents are them. escaping through a rent in the latter. of those important appendages the villi. Its substratum, also, is far poorer in lymph cells than that of the smaM intestine, and approaches more in character to ordinary fibrous connective-tissue. The epithelium consists of columnar cells similar to those of the ileum, but lacking pores in the but slightly thickened border. Goblet cells are also met Avith here (Schulze). Its muscular tunic resembles that of the mucosa of the stomach (§ 251), and exhibits the same variety in the relative development of its two layers (Schwartz, Lipsky). Imbedded in it we find a great number of tubular glands, the tubuli of the colon, and a variable number of lymphoid follicles like those already met Avith in the small intestine. The tubuli of the colon (fig. 491) are merely modifications of the follicles of Lieberkuhn from Fig. 493.—Tubuli from the colon , . . ... j n j i j of the rabbit, treated with which they are gradually developed. caustic soda. They present themselves in the form of simple undivided tubes with tolerably smooth and even walls, and a 498 MANUAL OF HISTOLOGY. and upwards, mm. More- Fig. 494.—Mouths of tubuiar glands from the colon of the rabbit, with radiating ar- rangement of columnar cells. length which varies between 0*4512 and 0*5640 mm. a the transverse diameter lying between 0*0902 and 0*1505 over, they are just as croAvded as the gastric and jejunal tubuli, and are found in every part of the large intestine, including the processus vermi- formis. They contain a viscid, and at times somewhat fatty mass (fig. 491 and 492, b), consisting of nucleated gland cells (measuring 0*0151-0*0226 mm.) made up of granular protoplasm. These present the appearance Avhen seen on the surface of flattened epithelium, from the fact of their being accommo- dated to one another, but are found on section of the gland to be columnar. Here also goblet cells may be encountered (Schulze). The mouths of these glands are of the ordinary kind, lined with columnar epithelial cells com*erging toAvards the lumen (fig. 494). The lymphoid follicles are, as a rule, larger than those of the small intestine. Their cupola? project from depressions in the mucous mem- brane. We have already remarked that their being croAvded together, in the vermiform appendix of the human being, lends to the latter organ a most peculiar appearance (§255). The vascular apparatus of the mucous membrane of the colon presents the same arrangement as that of the gastric mucosa, so that we may refer the reader to fig. 466. I he lymphatics of the mucous membrane of the colon were until very recently quite unknown, although the AArell-knoAvn network of the submucosa had been discovered long before. We are now certain of their existence in the mucous membrane of phytophagous and carnivorous animals, and it is highly probable that they are not absent in man. Though the surface of the colon is, as a rule, quite smooth, we find its upper fourth in the rabbit thickly studded Avith broad projections comparable to the in- testinal villi. These papillae, hoAvever (fig. 495), in contradistinction to the villi of the small intestine, are just as densely crowded with tubular glands as the other por- tions of the mucous membrane of the colon. In the axial portion of these pro- minences one or more blind lymphatic radicles are to be seen (f, g), precisely similar to those of the small intes- tine Descending perpendicularly, and twined about by a vascular net- work (a-d), they pass into the loose mesh-work of the submucous ymphatic vessels. In other animals the smooth mucous membrane of the colon is traversed partly by perpendicular csecal canals, and partly bv a wide-meshed net-work. These lymphatic vessels, which do not by any Fig 495.—Papilla from the colon of a rabbit, in vertical section, a, arterial; 6, venous twig of the submucosa; c, capillary net- work ; d, descending venous twig; e, hori- zontal lymphatic vessel ensheathing an artery;/, lymph canal in the axis; g, ciccal extremity of the same. ORGANS OF THE BODY. 499 means attain the same degree of development as those of the small intes- tine, have been traced down into the rectum. The lymphatic apparatus, on the other hand, attains in the vermiform appendix of man the most remarkable degree of perfection, as was first shown by Teichmann. The external ramifications of the absorbent vessels^ in the walls of the colon presents the same arrangement as in the small intestines, and the same complicated distribution is evident as in the muscular tunic of the latter. The nervous supply of the large intestine is derived from a wide- meshed submucous plexus beset with ganglia. The plexus myentericus presents the same peculiarities here as in the jejunum and ileum. No further reference need be made to the muscular and serous coats of the large intestine. At the anus the columnar epithelium suddenly ceases, Avhere the epidermial cells commence, Avith a sharply defined line of separation. Close to the termination of the gut below, a certain admixture of voluntary or striped muscle fibres presents itself among the unstriated elements like what is seen in the oesophagus. The mode of development of the mucous membrane of the colon is the same as that of the mucosa of the stomach (Koelliker). § 260. The physiological significance of the crypts of Lieberkuhn, and tubulai glands of the large intestine, is still a point of considerable obscurity. They are, hoAvever, supposed to secrete what goes under the name of the intestinal juice (succus entericus),—a fluid in the production of which the glands of Brunner, in the upper portion of the smad intestine, must also take a part. The secretion requires further examination. before Ave can pronounce upon its composition Avith any certainty. By a very ingenious mode of procedure, Ave have recently learned hoAv to obtain pure intestinal juice from the small intestine of dogs (Thiry). This is then found to be a thin, strongly alkaline secretion of a light wine colour, and sp. gr. of 1*0125. It possesses about 2*5 per cent, of solid constituents, of Avhich nearly 2*5 per cent, is albumen, and 0*3 per cent. carbonate of sodium. It dissolves fibrin as long as alkaline, but neither raw flesh nor boiled albumen are acted on by it. Moreover, it is said neither to convert starch into grape sugar, nor to decompose the neutral fats. This, however, is denied by Eiehhorst, as regards the secretion of the small intestine. The amount of this fluid poured out appears to be very great. The secretion of the tubular glands of the large intestine has also an alkaline reaction. The vermiform appendix is nothing but one large absorbent apparatus. §261. The pancreas, to Avhich Ave noAv turn, exhibits, as regards its structure, many points of similarity to the salivary glands. Its vesicles are roundish, measuring 0*0564-0*0902 in diameter. The membrana propria is studded over at certain points Avith nuclei, shoAving that here also, as in other kinds of racemose glands, the construction, probably, out of flat stellate C6ils The investing vascular network (tig. 496) is of the ordinary round form of the whole of this group of organs. 500 MANUAL OF HISTOLOGY. The numerous lymphatics require closer attention than has, up to the present, been bestowed upon them. The gland vesicles of the pancreas are clothed Avith cubical cells. In the full-groAvn rabbit these present in their inner half, or that next the lumen of the gland, fatty particles, Avhile the middle portion in which the nucleus lies, and external to the latter, is clear. The excretory canals possess rather thin Avails without muscular ele- ments, in Avhich are embedded, at the lower portion, a number of small racemose mucous glands seated in the mucosa. If we examine closely in animals the clothing of columnar cells, we find that from the beginning they are not particularly high. But in the branches they decrease more and more in length, until, finally, in the gland vesicles we meet with flattened epithelium, reminding us, in many respects, of vascular endotheUum. These are the centro-acinal cells of which we have already spoken in considering the salivary glands (§ 245). They were first seen here by Langerhans. By careful injection of the excretory canal-Avork, the same system of extremely fine secreting tubules may be brought to vieAv in the pancreas (fig. 297), as that to which wre have already so frequently alluded (Langerhans, Saviotti). As regards the nerves nothing certain is known. According to Pfiiiger their mode of termination is the same as in the salivary glands. The development of the pancreas takes place very early from the posterior Avail of the duodenum in the form of a small sac- cule or bud. As far as the composi- tion of the alkaline react- ing tissue of the gland is concerned, nothing is known. Its sp. gr. is, according to Krause and Fischer, 1 *047. A series of very interesting decom- position products, hoAv- ever, have been met Avith in the fluid saturating the gland; in the first place leucin in large quanti- ties, and a considerable amount, comparatively, of tyrosin (Virchow, Stae- Fig. 496.-vascular networiToftta pancreas from the rabbit. dfer> End Fr^ichs) ; fur- /r,? \ i- -, , . , ther, guanin and xanthin (Scherer) sarkin or hypoxanthin (Gorup), lactic acid, (and in the ox) inosite (Baedeker and Cooper Lane). Among these leucin (and tyrosin 1) have been remarked in the secretion of the gland, with which thev find their way into the intestinal canal. J In a state of rest, or, more properly speaking, of slow secretion, the g and in question appears pale. When, on the other hand, it is actively functionating, from about the fifth to the ninth hour after the reception of ORGANS OF THE BODY. 501 food into the stomach, it is of a deep red colour. In this condition bright scarlet blood flows from the veins of the organ, while in the inactive state the capillaries contain a dark fluid. The secretion of the gland or pancreatic juice (succus pancreatics) has been obtained from the living animal. So obtained, it is a strongly alkaline viscid fluid (Bernard), while that coUected from a permanent pancreatic fistula is a very thin liquid (Ludwig and Weinmann). Inthefirst al- bumen was digested (Ber- nard, Corvisart), starch was transformed into grape sugar, the neutral fats (after first forming an emulsion) were split up into glycerine and free fatty acids. In the latter form the first of these pro- perties was absent. The thick liquid, whose per- centage of water is about 90, is secreted by the gland when the latter is of a deep red colour from increased vascularity; the thinner liquid containing about 95-98 per cent, of water when it is pale. The amount of fluid secreted is greatest within thehoursbefore mentioned during digestion. It varies, however, to a great extent at other times, so that calculations as to the amount produced daily are found to differ considerably. The most essential constituents of the fluid consist, in the first place, of an albuminoid substance, which separates, in a gelatinous form on cool- ing below freezing point, from the thicker kind of pancreatic juice, but not from the thinner fluid; then, again, of a ferment occurring in both forms of the fluid, which converts starch very rapidly into grape sugar. Further, as Corvisart has pointed out, there is present in the first modifi- cation of the fluid another ferment Avhich digests albumen, and Avhose action does not cease on neutralisation, or even Aveak acidulation of the secretion (Kiihne). Finally, there is a third fermenting substance, which effects that peculiar decomposition of the fats already mentioned. The change also alluded to produced in the albuminates is of great interest, namely, a process of disintegration, with the formation of an albumen peptone, as Avell as considerable quantities of leucin and tyrosin (Kiihne). A gelatin petone has also been so obtained (Schweder). The constituents of pancreatic juice obtained by incineration, and amounting to 0*2-0*75 and 0*9 per cent., are lime, earths, magnesia and soda, chlorides of sodium and calcium, phosphates of sodium, calcium, and magnesium, sulphates of the alkalies, and traces of iron combined Avith Fig. 497.—Gland tubules from the pancreas of the rabbit, after Saviotti. a, strong excretory canal; 6, the same of an acinus c, delicate capillary passages between the cells. 502 MANUAL OF HISTOLOGY. phosphoric acid (Bernard, Frerichs, Bidder, and Schmidt). Sulphocyanide of potassium is not present in the secretion of the pancreas. § 262. We come iioav to the liver, the largest of all the glands connected Avith the digestive tract in man and the mammalia. Underneath its fibrous investment it presents, even to the unaided eye, a most peculiar appear- ance, OAving to its texture. A finer analysis of the latter shoAvs it still more distinctly to be alone among the glands of the body. If Ave carefully examine either the surface or a section of the liver, we notice markings which divide the former into regular fields. This is seen in many mammals very distinctly, but especially so in the pig and also the polar bear. The portions included in these markings are known as the hepatic lobules. They are separated from one another by narrow bands of lighter coloured substance, and are at one time of a dark reddish brown in the central portion, and of a lighter hue nearer their circumference, and at another quite the reverse, appearing light internally and dark externally. These differences depend entirely upon the state of the circulation in the organ. In man this marking is toler- ably easy of recognition in the infant's liver, but is, on the other hand, very indistinct in the adult. The diameter of the lobules may be roughly estimated, on an average, at 9 mm., and about a third more in larger indi- viduals, while, in some cases, they may only measure IT mm. Each of these lobules consists essentially of innumerable gland cells, and an exceedingly complex network of vessels passing among them, and tending all towards one central point, where their confluence forms the commencement or radicle of an hepatic tAvig, while externally they are bounded by branches of the portal vein and biliary canals. The hepatic elements are distinct from one another (fig. 498), and pre- sent great similarity to peptic cells. Their form is more or less irregularly polygonal, owing to their mutual accommodation. In diameter they are, on an average, about 0*0226- 0*0180 mm., with extremes up to 0*0282 mm. and down to 0*0113 mm. Their nuclei, which are oval, and contain nucleoli, have a diameter of 0*0056- 0*0074 mm. Each cell usually contains one of them (a), but may in some cases be possessed of two (b). The substance of which the hepatic cells are composed is of viscid consistence, and presents a greater or less number of fine elementary granules embedded in it. The cells are entirely destitute of membranous cover- Fig. 498.-HePatic ceiis j?g' and th" ^Jf stracture .when isolated, is seen to of man. a, with one De possessed ot the power of amoeboid motion, very ^ftoetatto.*"11 d[stinc}> though slow (Leuckart). Besides these just mentioned, other matters are fre- quently met with in the contents of the hepatic cells, which, when pre- sent in small quantities, may be regarded as normal constituents, while their appearance in greater amount denotes a morbid condition of the cell. These are, in the first place, molecules of a brown or yellowish- brown pigment (biliary colouring matter), and, secondly, fatty globules of varying sizes (fig. 500). The latter, chiefly in'the form of very fine fatty molecules, are found normally in sucking animals and children and ORGANS OF THE BODY. 503 may be called into being artificially by the administration of very rich fatty food to an animal. In very well marked specimens considerable masses of fat are to be seen filling the whole of the cell, and completely obscuring its nucleus. The cells in such cases are often increased in size. Amongst adults, and especially after habitual indulgence in rich food, such fatty livers are of frequent occurrence. But besides this fatty infiltration, as it may be called, of the hepatic cells, which the latter are well able to tolerate, regaining their previously normal condition as soon as freed from the oily molecules, there is also a true fatty degeneration, a morbid change of the whole ele- ment into lardy matter, which leads to its entire destruction. The arrangement of the cells of the lobules is very remarkable. They are placed in long rows side by side and connected with one another at points, without by any means being fused to- gether. This arrangement, in elongated groups, may be fre- quently recognised among hepatic cells which have been scraped off the cut surface of the liver (fig. 498), but more clearly in delicate sections of the lobules, as in fig. 499, in which a radiat- ing arrangement of the bands of elements is perfectly manifest, especially in the more internal part, while externally this is more or less lost, the cells being disposed with greater irregularity. In the human and mammalian liver generally, the cells of such a band are arranged in a single row, only doubled at certain points. Much variety exists, however, in the mode of grouping. These so-called lobules, which do not, however, like the well-known divisions of racemose glands, open into an execretory duct, but are placed on a twig of the hepatic vein, are separated one from the other (at those points at which they are seen sharply defined) by distinct septa of connective-tissue, which may be isolated from about the lobules in the form of regular capsules. This mesh-work of connective-tissue is derived, in the first place, from the so-called capsule of Glisson, i.e., that sheath of cellular tissue which clothes the blood-vessels and bile ducts, entering the organ at the porta hepatis, and again from the connective-tissue covering the whole organ. In the normal condition of the human liver this septal connective-tissue, dividing lobule from lobule, is very scanty, while, in a certain peculiar affection of the organ, known as cirrhosis, it becomes hypertrophied. §263. In order to gain a farther insight into the structure of the organ, it will 33 Fig. 499.—Hepatic lobule from a child ten years old (copied from Ecker), with the central hepatic vein in transverse section. Fig. 500.—Cells from a fatty liver, a, b, filled with smal oily particles and globules c, d, with larger drops. 504 MANUAL OF HISTOLOGY. be necessary, in the first place, to consider the arrangement of its blood- vessels. The vascular system of the liver possesses this peculiarity, that it receives its blood from two sources, namely, from the hepatic artery and portal vein. The last of these conveys a much larger proportion of blood to the organ than the former, Avhich takes part less in the elaboration of bile than in the nutrition of the hepatic tissue. Its branches, accompanying the divisions of the portal vessels and bile ducts, are distributed, in the first place, as vasa nutrientia to the coats bf both (rami vasculares) ; and, secondly, to the serous covering of the liver, as far as Avhich they pene- trate (rami capsulares), forming there a wide-meshed capillary netAvork. The veins derived from these empty themselves into the ramifications of the portal vessels, so that the latter may be injected from the hepatic artery, and vice versa, if the canula be inserted into the portal vein the injection may be driven into the hepatic artery. Finally, a few very small twigs (rami lobulares) sink into the peripheral portion of the capil- lary network of the hepatic lobules. Through these the hepatic artery takes some part, at least in the production of the bile. The portal vein, with whose course we take it for granted the reader is already acquainted from the study of general anatomy, forms, with its terminal branches, the venrn interlobulares of Kiernan, or vena} periphericas of Gerlach. These are fine tubes of 0*0338-0*0451 mm. in diameter, which surround the lobules either in the form of short (in man) or long (rabbit) loops, or, as is pre-eminently the case in the pig, in the form of regular rings, breaking up rapidly on all sides, either into finer branches or immediately into capillaries. In fig. 501 Ave have a representation of what takes place here : a twig of the portal vein is seen passing through the middle, and giving off on either side the rami-interlobu- lares, Avhich terminate eventually in a capillary network after en- circling the lobules. This network, the most highly developed Avhich exists in the body, consists of vessels from 0*0090 to 00126 mm. in diameter, whose delicate walls can only with diffi- culty be demonstrated. The meshes formed by these are very dense, mea- suring only from 0*0226 to 0*0451 mm. They are either rounded, square, or triangular in figure, and lie, for the most part, with their long axis, often rather indistinctly directed, towards the centre of the lobules. In the interior of the latter the capdlaries either form, by their rapid confluence, a single hepatic venous radicle, or, what is more frequently the case, two or more such. Ihese may, m some instances, be met with in much larger num- bers. The hepatic twigs are situated in the centre of the lobules • thev are from 0*5640 to 0*0677 mm. in diameter (Gerlach), and have been Fig. 501.—Rabbit* liver injected, showing a portal branch, the vena; interlobulares, the capillary net- work, and a vena intralobularis in the centre of a lobule. ORGANS OF THE BODY. 505 named by Kiernan, on account of their position, the venas intralobular, by Gerlach venas centrales. On their exit from the lobules these vessels join together to form larger trunks. The latter are intimately connected with the parenchyma of the organ, so that they remain gaping even when emptied From the fact that the veins of the liver do not possess valves, the whole hepatic circulation may be just as easily injected from them as from the portal vessels. §264. So far we have only discussed those points of structural arrangement of the hver which are easily recognisable, and may be therefore regarded as permanent additions to histological knowledge. Far different is it now, however, Avhen Ave come to deal with questions as to the nature of the sustentacular substance of the interior of the lobules, Avith the relations of the veins to the finest biliary ducts, as well as the disposal of the radicles of the lymphatic system in the parenchyma of the gland. From the fact that the two networks—that formed by the intersection of bands of hepatic cells and that of the circulation—are closely inter- Avoven one Avith another, many suppose that the hepatic cells are simply entangled in the meshes of the capillary network. Nevertheless, if very fine sections of a properly hardened liver be care- fully brushed with a camel's hair pencil, there remains, after removal of the hepatic cells, an exquisitely delicate reticulated frameAvork, com- posed of homogeneous membranous bands, which separate the rows of gland cells and blood stream from one another. In this network may be seen, in the first place, the nuclei of the capillaries, and then, small isolated nuclei, Avhich present them- selves in a shrunken condition in the adult (fig. 502). In the liver of the infant, or foetus, in the later months of utero- gestation, this fine transparent membranous structure may be seen at certain points to be double. One of its layers corresponds to the Avails of the capillaries, and in some instances has been resolved into those vascular cells so well known (p. 363) (Eberth). Its other lamina, on the other hand, invests the bands of hepatic cells as they intersect each other. From this it would appear to be beyond doubt that a thin homogeneous layer of sustentacular connective-substance envelopes the various toavs of hepatic cells. This layer is often of the most extreme delicacy, but may be seen with comparative ease to be continuous at the periphery of each lobule Avith the interlobular connective-tissue. Here then Ave have the long sought for membrana propria of the hepatic cells presenting itself. To it belongs indubitably the second and smaller series of nuclear formations, which appear at an early period in greater abundance, as a system of connective-tissue corpuscles, frequently exhibiting distinct cell bodies. While at first these tAvo membranes, namely, the sustentacular connec- ndc Fig. 502.—Sustentacular tissue from the liver of the infant, a, homogeneous membrane with nuclei; b, filiform folds in the former; c, isolated hepatic cells, remaining after brushing. 506 MANUAL OF HISTOLOGY. tive-substance of the gland and the Avails of the vessels, appear quite distinct from one another, they assume the appearance, later on in older animals, of being fused into one single lamina. That this, however, is probably not the case, will be seen further on when we come to consider the arrangement of the lymphatic streams. For our acquaintance with these important points, in regard to the structure of the liver, we are indebted for the most part to the exertions of Beale and E. Wagner. § 265. The arrangement of the ultimate radicles of the bile ducts in the interior of the lobules, and their relations to the secreting cells, is a subject fraught Avith difficulty for the microscopic anatomist, and one which for a long time baffled every attempt at elucidation, owing to the imperfection of the earlier methods of treatment of the hepatic tissue. It is no Avonder, then, that here extensive use was made of hypothesis, and that many theories as to the arrangement of parts sprung up only to be aban- doned again. At last success attended the efforts of some to demonstrate distinctly the finest bile ducts. The first successful observers in this interesting field of discovery were Gerlach, Budge, Andrejevic, and MacGillavry. The results of their investigations were all very similar, and our own experiences, as well as those of Chrzonszczewsky (arrived at by means of a peculiar method of treating the hepatic tissue), are in exact accordance with them. Further progress in this direction was made again through the elegant demonstrations of Hering, confirmed and amplified later on by Eberth. Subsequently similar passages were discovered in the various racemose glands, to which we have already frequently referred (§§ 198, 245, 255, and 261). The first point to be noticed, and one which has long been recognised Avith ease, is that the ramifications of the bile ducts accompany the branches of the portal vein between the hepatic lobules. From these, Fig. 503.—Biliary capillaries from the rabbit's liver. 1. A part of a lobule • a vena. hepatica; b, portal twig; c, bile ducts; d, capillaries; e, biliary caniliarios 2. Biliary capillaries (6) in their relation to the capillaries of the vascular system (a). 2. Biliary capillaries in their relation to the hepatic cells; a caDillaries• ft hepatic cells; c, bile ducts; d, capillaries of the blood-vessels. ' then, another set of fine thin-walled biliary canals take their rise (fig 503, 1), which invest the further ramifications of the vena porta? (b) with delicate netAvorks (c) in their course between the lobules. ORGANS OF THE BODY. 507 More internally still these tubules are continuous Avith an exquisitely delicate> mesh-work of the finest tubes, known as the biliary capillaries (d). lhese are^passages of extremely small calibre, measuring in the rabbit only 0*0025-0*0018 mm. Arranged in a dense network (3 a) they pass between the hepatic cells (b) in such a way that the sur- face of each of the latter comes in contact with them at various points. The meshes are cubical, so that the network presents the same appear- ance from almost every point of view. The breadth of each mesh is on an average, 0*0144-0*0201 mm. in the rabbit, and corresponds as a rule with that of the gland cells. The whole is characterised by the wonder- ful delicacy of arrangement, and the regular way in which this third and finest network is interwoven with the two others formed by the blood capillaries and bands of gland cells. These biliary capillaries have been knoAvn for many years past to exist in many mammals, among Avhich the rabbit appears to be best suited for their demonstration. They have recently, however, been dis- covered in the other three classes of vertebrata also (Eberth, Hering). The questions now arise—Do the biliary capillaries possess independent walls, or are they simply lacunar passages; and Avhat relation do they maintain to the hepatic cells ] For our own part, we would with MacGillavry, as formerly, so still ansAver the first question in the affirmative, having ahvays held the opinion that the biliary ducts do possess independent walls. Isolation of the latter has, however, up to the present been impossible, but the si°ni- ficance of this fact seems of minor importance when Ave consider the great delicacy of all the component tissues of the part. Again (2), the interlacement of the blood capillaries (a) is seen to take place in such a peculiar manner through the network of the biliary capillaries (b), and in many localities the latter present such regularity when injection has been successfully accomplished, that the existence of a system of lacunae of this kind between cells endowed with vital contractility seems highly impro- bable. Further, we may at times encounter points, at the junction of injected and uninjected portions of tissue, at which the amount of granules of colouring matter of the former diminish in the latter in a Avay that permits of our following on the network of biliary capillaries a little farther by the thin lines of coloured fluid, until they appear eventually in the tissue around the several hepatic cells quite destitute of coloured con- tents. Under very high magnifying power, also, the empty netAvork may be seen clearly, presenting great regularity, the canals of the same calibre throughout, with no enlargements at the nodal points, and sharply con- toured. Sometimes Ave are even so fortunate as to obtain a section so thin that it is almost entirely formed of a network of bands of hepatic cells only one tier thick; and here, along the middle of each band, some of these bdiary passages may take their course, maintaining the axis, and lying quite free and uncovered by other toavs of cells. An appearance of this kind is easily explained, if Ave accept the presence of a special Avail to each canal, but is, on the other hand, difficult to account for if the pas- sages be regarded as lacunar. The existence of these Avails has been since recognised by both Eberth and Koelliker. The next question is : Hoav are these biliary ducts related to the hepatic cells ? On this point the opinions of histologists have until recently been very 508 MANUAL OF HISTOLOGY. much divided owing to the obscurity of the subject. Many (as, for instance, Andrejevic some years ago) supposed the bodies of the hepatic cells to be always interposed between the blood and biliary capillaries, so that these two could never come into contact one Avith another. MacGillavry, on the other hand, believed in the interlacement and Aveaving together of both networks in such a Avay as to render this possible. The discoveries of Hering and Eberth, however, have since given sup- port to the first view, which, from our own researches, we are also led to believe to be the correct one. But in order to understand this fully, we must examine not only the complex liver of the mammal, but the gland also in a simpler form, as it presents itself in other verte- brate animals, among which Ave Avould reckon for the case before us not only fishes and amphibia, but also birds. Let us take, then, first of all the liver of the amphibia, which is especially instructive. Here Ave find—as, for instance, in the common ringed snake—that the bands of cells and netAvorks of these bands are made up (as is shoAvn in fig. 504, 1) of rouleaux of gland cells, bounded exter- nally by blood-vessels, and con- vergent toAvards a fine biliary duct running through the axis of each rouleau. One of the latter is in transverse section comparable to an ordinary tubu- lar gland clothed with unlamin- ated epithelium, and possessed of a very narrow lumen, each blood capillary being separated from the bile ducts by the full height of the hepatic cells (Her- ing). The livers of the batrachia, also, present a similar arrange- ment of parts. A side-view (2) discloses betAveen each two toavs of hepatic cells a long bile-duct holding the axis of the bands formed by these rouleaux, while external to the latter the blood- capillaries are situated. Nearer the circumference of the organ biliary ducts of greater calibre are to be found clothed Avith low columnar epithelium which has taken the place of the hepatic cells. _ Among the lower orders of vertebrate animals lateral branches on the bile ducts are seen, but sparely, and the existence of blind terminations to Fig. 504.—Ultimate radicles of biliary ducts in the liver. 1. From the common snake (alter Hering). 2. From the salamander (after Eberth). 3. From the rabbit, a, blood-vessels; 6, hepatic cells; c, biliary capillaries. ORGANS OF THE BODY. 500 these (although liable to be simulated by imperfectly injected canals), can- not be denied in our opinion. It is only Avhen we ascend to birds, that we meet with a higher deve- lopment of this system of lateral branches. Among those mammals, on the other hand, which have been hitherto made the subject of research, it is in many cases found in an extremely high state of development in the form of that exceedingly complex network of biliary capillaries, represented in fig. 503. Here the surface of each hepatic cell comes in contact with one or more biliary ducts. But even still, and though presenting complex and various modifications, the funda- mental plan, as seen in fig. 504 (3), remains distinct. The biliary (c) and blood-capillaries (a) never come into actual contact; they are always sepa- rated from one another by a Avhole or fraction of an hepatic cell (b). In the loAver vertebrates several hepatic cells combine to enclose the former, Avhile higher up the scale the contact of fewer, and at last of two, is suffi- cient for their formation. Finally, we are met by the inquiry, What is the nature of the delicate wall of the biliary duct? The cuticular border of the epithelial cells in the terminal ramifications of the bile ducts, is pointed out by Eberth as its probable source. Just as the cell secretion or cuticular formation becomes thickened and perforated by pores toAvards the larger branches, as already mentioned (§ 92), so does it, as we advance upon the biliary capillaries, acquire greater delicacy, forming eventually the walls of the biliary capillaries at the points of con- tact of the hepatic cells. § 266. ' There are still left for our consideration the larger biliary ducts, the lymphatics, and nerves of the organ. Resembling to a considerable extent the ramifications of the portal system, in their course and mode of confluence, the bile ducts present for our consideration a homogeneous membrane with a clothing of small Ioav cells from the ductus interlobularis, Avhich has been already mentioned in the preceding chapter. In the larger trunks, instead of homogeneous Avails, fibrous coats and long cylindrical epithelial cells make their appear- ance, upon whose surface a porous cuticular border may be recognised with increasing distinctness, as Ave advance from within outwards. In those passages of large size, which have already left the parenchyma of the liver, a mucous membrane and external fibrous layer are to be seen composing their Avails. It was formerly supposed that, besides these, a series of longitudinal contractile fibre cells entered into the structure of the tube : this has not, however, been since confirmed. The coats of the gall bladder are formed, according to Henle, of layers of connective-tissue alternating with muscular laminae, consisting of unstriped fibres which cross each other in all directions. The mucous membrane is marked by beautifully regular folds, and is covered by the same coating of nucleated columnar cells met with in the small intestine. These latter are also endowed Avith the same poAver of absorbing fats as those of the intestine. The bile ducts possess also numerous follicles and racemose glands. The first are to be found in the larger canals, as in the ductus eholedochus cysticus and hepatic duct with its larger branches: they are arrangea sometimes irregularly, sometimes in toavs. The racemose mucous glandt, 510 MANUAL OF HISTOLOGY. are but sparely found in the gall bladder and inferior portion of the c stic due , but make their appearance in the upper portion of the canal and ductus choledochus and hepaticus (fig. 505, a) In the wider passage ofthe latter, with a diameter of about 0*7 mm., is to be found another series of simple cical formations, some of tubular, some of flask-like figure In that network of fine passages situated iu the transverse fissure of the liver they occur also (6); likewise in those ducts arranged around the laiger branches of the portal vein Avithin their sheaths, and finally in the lateral tAvigs given off from the branches lying in the longitudinal fissure of the organ. These appendages have by some fg^ been supposed to be im- perfectly developed mucous glands, but by the majority of histologists they are re- garded noAV as blind rami- fications of the bile ducts or receptacles for the bile (Beale, Koelliker, Riess). According to this last vieAv they would be numbered among the vasa aberrantia of E. H. Weber. We understand under this name, passages of 0*02-0*7 mm. in diameter, which leaving the substance of the liver, undergo sub-divi- sion into smaller branches in a connective - tissue stroma. They are to be found in the ligamentum triangulare sinistrum, and the fibrous bridge across the inferior vena cava. They are partly disposed in a retiform manner, and some of them terminate with bulbous dilatations. The numerous lymphatics of the liver consist of a series of superficial vessels, and another situated more deeply communicating Avith the first. The first lying in the deepest layer of the peritoneal covering of the organ, is made up of a complex unlaminated network of fine canals, Avhose larger efferent vessels pass off in various directions. Those on the convex surface of the liver take their course towards the ligaments of the organ, and do not meet with lymphatic glands until their entrance into the thorax. Those from the under surface of the viscus, on the other hand, empty themselves into lymph nodes in the neighbourhood of the trans- verse fissure and the gall-bladder. The deeper lymphatic vessels enter with the portal veins, hepatic arteries, and bile ducts, into the interior of the organ, enveloped in a fibrous prolongation of Glisson's capsule, and follow all the ramifications of the latter canals. In their course they invest the branches of both ducts and blood-vessels with a delicate network of tubes, and arrive thus at the periphery of the lobules, still in the form of distinct vessels. Here Fig. 505.—a, bile-duct glands from the hepatic duct of the human liver; b, injected twig of the biliary plexus of the fossa transversa (after Henle). ORGANS OF THE BODY. 511 they merge, either as distinct vessels or interlobular lacunae, into a very remarkable netAvork of lymphatic passages, traversing the whole lobule in every direction. Every blood capillary, namely, is ensheathed in a lymph stream, whose external boundary is Avithout doubt formed by the delicate fibrous sustentacular membrane of the hepatic cell bands; so that each of the cells of such a band bounds, Avith a portion of its surface, the .inter- lobular lymph stream. We are indebted to MacGillavry for the discovery of these perivascular lymphatic spaces (§ 207). These facts we have confirmed by personal observations, and Biesiadecky has recently succeeded in demonstrating that the same arrangement of parts prevails in the human liver. Incautious injection of the biliary capdlaries frequently results in rupture of the latter, and communication betAveen them and the lymphatic interlacements, giving rise to appearances which have led at least several observers into the error of regarding the latter as biliary netAvorks. The nerves of the liA*er, springing for the most part from the plexus cceliacus, and consisting of both Remak's fibres and other dark, fine, or broader filaments, spread themselves along the course of the bile-ducts, along the hepatic arteries and its ramifications, as far as its interlobular branches, along the portal and hepatic veins and serous covering of the organ (Koelliker). The mode of their ultimate termination is still very obscure. § 267. Turning now to the composition of the liver, older and rougher analyses of its tissue (whose sp. gr. is stated by Krause and Fischer at T057) give, beside about 70 per cent, of water for man, soluble albumen, coagulated protein matters, glutinous substances, fats, extractives, and about 1 per cent, of mineral constituents. In addition to these, a number of interesting mutation products have been found in the fiver. As far as we knoAv at present, glycogen, grape sugar, inosite (in the ox), lactic acid, uric acid, hypoxanthin, xanthin, and urea haAre been met with here. Kreatin and kreatinin, on the other hand, have not been found, nor leucin and tyrosin, of which the first is at the most only present in traces in the healthy liver (§ 31 and § 32). Cystin has also been found in the organ under morbid conditions. None of these matters are present in the bile, and must consequently return into the circulation. The mineral constituents are, in the first place, phosphates of the alkalies, which appear in large quantities, the salts of potassium prepon- derating, while phosphate of calcium and magnesium, chlorides of the alkalies and sulphates are present in but small amount. Iron, manganese, and copper (p. 62b with traces of silicates, have also been found. Accurate observation has shown that the tissue of the liver, which is of soft consistence during life, possesses also an alkaline reaction, while in the dead animal it reacts acid. . The glandular elements, or hepatic cells, are composed of richly albu- minous protoplasm, containing frequently glycogen. This latter com- pound vanishes from the cells of starving animals. Glycogen, which is neither found in the vegetable kingdom nor in the blood, must be regarded as a product of cell life. Through the agency of a ferment also existing in the ceU, this substance is converted first into dextrin, as an 512 MANUAL OF HISTOLOGY. intermediate step, and then into grape sugar. Its amount in the living cell is so small that Ave are unable actually to prove its presence there, but immediately after death it increases considerably in quantity. Besides this, fatty matters are encountered in the glandular elements, and frequently also biliary pigment in the form of granules. The hepatic cell, however, fabricates besides several other substances of great importance in the formation of bile, as we shall see presently in considering this secretion. It is not improbable that the formation of glycogen, and certain of the constituents of bile, are only different portions of one and the same mutative chemical process. The fatty matters of hepatic tissue still aAvait accurate analysis. § 268. The bile, an exceedingly decomposable secretion, is, as it flows immediately from the liver, a clear and rather thin fluid of alkaline reaction. Its colour is sometimes reddish yelloAV, as in the carnivora, and sometimes greenish, as in the case of the vegetable feeders. What- ever its tint be at the outset, it always turns to green on exposure to the air. To the taste it is sweetish bitter, leaving little aftertaste. During its sojourn in the gall-bladder its characters become changed, its alkalinity appears more marked, it receives an admixture of mucus, the colour deepens to brown, and it becomes more concentrated. The sp. gr. of human bile is usually accepted as 1*026-1*032. The fluid is usually completely homogeneous, without either granules or fat globules ; nor do hepatic cells make their appearance in it, owing to the small calibre of the biliary capillaries. The most important and essential constituents of bile are the com- pounds of sodium with two peculiar acids, and the pigmentary substances. These two acids, taurocholic and glycocholic, have been already considered (§ 27). From the fact that they are absent from the blood, we are forced to the conclusion that they are generated in the liver. Their mode of origin, hoAvever, is still a matter of great obscurity. For a long time the greatest uncertainty prevailed as to the nature of the colouring matters of the bile. It was not until after Staedeler's beautiful investigations Avere published that any progress was made in this direction (p. 53). Fresh bile appears to contain only tAvo of those pigmentary matters discovered by this chemist, namely, the more essential bilirubin and biliverdin. Bilirubin (fig. 506) may be obtained from slightly acidulated bile by agitation with chloro- form. That it is nearly allied to haematin, and has its origin in the destruction ofthe pigment of the blood-cells in the parenchyma of the liver, can hardly be doubted, although we were obliged at p. 50 to negative the question of identity of the tAvo substances. The peculiar crystalline form of this pigment is also against our accepting it as identical with haematin, its crystals assuming a Avhetstone fi«ure. Very small crystalline bodies" made up of bilirubin in irregular and sometimes stalk-like masses, may be met with in the bodies of the hepatic cells at times. Pig. 506.—Crystals of bilirubin obtained from its solution in sulphide of carbon. ORGANS OF THE BODY. 513 The enormous colouring power possessed by this pigment is also a point of great interest. Diluted to a million times its volume, it is still capable of communicating a distinctly yellow tinge to a layer of fluid two inches deep. Again, as is well known, a very small quantity in the blood of jaundiced persons imparts a yellow colour to their skin and con- junctiva. The pigment of fresh green bile is probably biliverdin, nearly allied to the last. It is also developed in the other species of bile on their becoming green. Dissolved in alkalies, it gradually assumes a brown tint. In decomposing bile, another brown colouring matter is also to be found, which, on the addition of acid, assumes a green colour. This is probably biliprasin. We have already referred, as far as necessary, to the mode of generation of the various colouring matters (§ 37). Another colouring matter, also present in the urine, has likewise been recently discovered in this fluid, to which the name of urobilin (§ 53) has been given (Jaffe). Besides these constituents, neutral fats are also present in the bile, also combinations of fatty acids with alkalies, lecithin, Avith its two decomposition products, glycero phosphoric acid and neurin or cholin, cholestearin (p. 30), and mineral matters. The latter consist principally of chloride of sodium, some carbonate and phosphate of sodium, phosphate of calcium and magnesium, as Avell as traces of iron, copper, manganese (p. 62). Fresh bile contains no sulphates ; these are, however, produced in it by incineration and by the processes of putrefaction, from taurin, which contains sulphur (p. 49). Of gases, the bile contains (dog) a small amount of oxygen, abundance of carbonic acid, and some nitrogen (Pfiiiger). The proportion of these matters in the bile is usually higher than in the other digestive fluids, but varies greatly, according as the bile remains for a longer or shorter time in the gall bladder, Avhere it undergoes a loss of water by absorption. The percentage of solid constituents in the human bile is generally estimated at from 9 to 17 (Frerichs, Gorup). That from the ox contains from 7 to 11 per cent,, that obtained directly from the livers of dogs, cats, sheep, only about 5 per cent. (Bidder and Schmidt). The bile of the Guinea-pig is still richer in Avater. The organic matters in man amount, according to Frerichs, to about 87, or, according to Gorup, to 93 per cent, of the dried residue. Among these the combinations of sodium, with the two biliary acids, appear to pre- ponderate greatly, while the proportion of fats and of cholestearin is much less considerable. The percentage of mineral constituents is stated by Gorup to be about 6*14 of the whole solid residue. The secretion of bile in the normal conditions of the system is con- tinuous, but liable to vary considerably. It depends, in the first place, on the nature of the alimentary matters taken into the system, being most abundant after a meal of flesh mixed with fat, while it decreases after purely fleshy food, and is still less after an exclusively fatty diet. V draught of water also increases its amount, and after the introduction of food°into the system, the quantity elaborated becomes larger and larger for several hours. The quantity of bile produced in twenty-four hours varies in many animals and has besides been estimated differently by several observers for one and the same animal. From 1000 to 1800 grammes is supposed 514 MANUAL OF HISTOLOGY. generally to be about the average amount secreted by the adult human being daily; though we must admit that this statement is based upon very uncertain data. As to the use of bile in the processes of digestion, we know that it possesses no fermenting power over the albuminates, but precipitates on the contrary albuminous substances from their acid solutions whether digested or undigested. It has the same effect on pepsin. It is still a debated question,'' whether it possesses the poAver of transforming starch into sugar. It saponifies the free fatty acids, and forms an emulsion with fat, thus facilitating its absorption by the intestinal villi (Bidder and Schmidt, Wistinghausen). Besides this, as Bidder and Schmidt have shown, the greater part of the bile, in fact almost ad its water, as well as f ths of its solid constituents, is again taken up into the circulation by absorption from the intestines ; but nothing farther is known as to what changes its constituents undergo there. In a changed state the pigmentary matters pass through the intes- tine, together with a small quantity of cholestearin, and occasionally some taurin. The products of the metamorphosis of choleic acid are also met with, namely, choloidinic acid and dyslisin. Neurin also and glycero- phosphoric acid also partake of the nature of decomposition products. The development of the liver, although still a knotty point in his- tology, has been cleared up to a great extent by the important dis- coveries of Remak. From these it would appear that the organ springs very early from the cells of the so-called gland layer in the form of two saccules, clothed externally by a fibrous envelope, derived from the walls of the intestine, and which has been pushed before the growing saccules. From the most internal cells of these primitive bile ducts, solid groups of elements are produced by a process of division, the " hepatic cylinders/' which advance in their farther groAvth into the external enveloping layer, dividing in their progress, and branching with the formation of networks. Those cells of the originally external envelope, which haAre become as it were entangled Avithin the meshes of the network formed by the hepatic cylinders, are gradually converted into fibrous or connective tissue, vessels and nerves, while the secreting elements of the gland are to be found in the cells of the hepatic cylinders. It is a fact of great interest, first pointed out by Bernard, that at an early period of intra-uterine existence the liver contains no glycogen, although this is to be found in the placenta, the epidermal cells, and epithelium of the intestine, as well as in the passages of the glands developed from the latter, and also in muscle (§ 170). With the development of the liver the disappearance of glycogen commences at one point early, at another later, continuing until birth. 4. The Urinary Apparatus. § 269. The urinary apparatus consists, as is Avell knoAvn, of two glands: the kidneys (designed to secrete the urine), and a system of excretory pas- sages made up of the ureters, which terminate in a common reservoir the bladder, and the urethra, by which the fluid is eventually carried off from the latter. The kidney, Ren, a large bean-shaped organ with a smooth surface is covered by a thin but strong fibrous envelope, the tunica propria, which is continued on to the external surface of the infundibula at the hilus ORGANS OF THE BODY. 515 Avhere the ureter leaves the gland, and its nutrient blood-vessels enter. The substance of the kidney presents for consideration tAvo portions, namely, the cortical or external, which is of a broAvnish red colour, and in- distinct structure to the naked eye, and an internal paler medullary portion of fibrous appearance. The latter is marked by fine lines converging towards the hilus, and consists in most mammals of a single conoid mass with the apex toAvards the hilus, but in the case of the human being and pig this is divided into from 10 tofc15 sections, Avhose bases lie towards the cortical part of the organ, their apices being directed toAvards the hilus. To these the name Malpighian or medullary pyramids has been given. Between them the cortical substance is prolonged inwards in the form of septa, known as the columns Bertini, Avhile both portions of the organ contain interstitial sustentacular connective-tissue. Notwithstanding their want of similarity in appearance, both portions of the kidney consist of glandular elements resembling each other in many particulars. These are long branching canals or tubes, known as the urinifer- ous tubes of Bellini. In the medullary part of the organ, however, they pursue a straight course diverging slightly or run- ning nearly parallel, and dividing at very acute angles; while on their arrival in the cortex they commence to turn and twist upon themselves, and intertwin- ing one with another (fig. 507, e), terminate eventually in a blind dilatation (d) which enve- lopes a peculiar congeries of vessels (c*, c1). The difference of texture ob- served in both portions of the organ is thus explained. This is all that was known -,,,.«• f until recently about the structure of the kidney, and much difference of opinion existed, besides, as regards the relations of the blood-vessels to the several elements of the organ. • * * +i,a *+„,q„ We owe much to Henle for having given a new impetus to the study of the histology of this organ some years ago by his interesting dis- coveries. He found, namely, that the medullary substance contains besides the well-known straight tubes, with acute-angled division, which open into the pelvis of the organ, a series of finer canals arranged in loops, whose convexities are directed towards the apex of the medullary pyramids and which on arrival at the limits of the latter are continued into the cortex. Fig. 507.—From the cortex of the human kidney, a, arterial twig giving off branches; 6, to the con- geries of vessels c*. c1; c, efferent vessel of the latter; d, dilatations on the ends of convoluted uriniferous tubes, e. 510 MANUAL OF HISTOLOGY. But Henle's work on the subject, besides elucidating much that was most useful, led to incorrect conclusions as to the structure of the cortex. It served, however, a great purpose in provoking a series of farther inves- tigations, and thus through individual exertions the views on the struc- ture of the organ have undergone since a most salutary change. Remarks.—(1.) Among the older essays on the subject which may be said to extend up to the year 1862, we shall only mention, beside the German Avorks of Ger- lach, Lvdwig, and Koelliker, those of Bowman in the Fhil. Trans. Act. for the year 1842, pt. i. p. 57, and Johnstons article "Ren" in the Cyclopedia vol. iv. p. 231. §270. Turnino* now to the medullary pyramids, whose apices have received the names of papillce renales, we find the latter studded with the open- ings of the excretory canals. The number of these oval orifices for each papilla is from 10 to 30. They correspond to a similar number of trunks of the gland tubes (fig. 508, a). The latter are, however, very short, and almost in the immediate neighbourhood of their mouths each begins to divide usually at very acute angles into two or three branches. These again split up into several more (b, c, d, e) until the whole assumes the appearance of a bunch of twigs. In the most peripheral groups in the human kidney each tube presents to a certain extent the appearance of a runner with somewhat knotted branches creeping for a greater or less distance along the ground (Henle). With this rapid sub-division the canals become considerably narrower. While the mouths and primary trunks possess a calibre of 0*3-0*1985 mm., the diameter even of the first series of branches sinks to 0-1985-0*0990 mm., and in the next in order to 0*0510-0*501 mm. This is the diameter of the uriniferous tubes at about two lines from the apex of the papillae, and which they continue to maintain throughout the rest of their slightly divergent course through the medul- lary substance. Further division is noAv no longer remarked, or if seen is only exceptional. The increase in bulk of the medullary pyramids towards the cortical por- tion of the organ is partly explained by this division and subdivision of the uriniferous tubes, but only partly so. Another factor in this enlargement of the bases of the pyramids is the system of narrow, looped, uriniferous tubes (Henle), Avhich appear here in addition to those opening at the papillae, and to which the name of canals of Henle has been given (Koelliker). These, from 0*04, to 0*02 mm. in diameter, pass in great numbers out of the cortex into the medullary portion, and are here, doubled back upon themselves sooner or later (i.e., at a greater or less distance from the papillae), forming regular loops. Thus they return to the cortex, becoming wider in their course back again. In order now to prevent all misun- derstanding m the rather complicated explanation of the arrangement of parts about to follow, we shall apply to those limbs of the looped canals Fig. 508.—A uriniferous tube with its branches from the medullary substance of a new-born kitten's kidney (prepared with hydro- chloric acid), a-e, divisions from the first to the fifth order (original drawing from Schweigger-Seidel). ORGANS OF THE BODY. 517 which leave the cortex of the kidney the term curving back again that of recurrent tubes. In fig. 509 we have a representation of these looped canals (d) lying between the widely sepa- rated tubes (b, c). It shows likewise the in- equality in the distances from the papillae, at which the smaller tubes turn on themselves. It seems hardly necessary to remark that the number of looped tubes increases the nearer Ave approach the cortex of the organ. This is shoAvn by transverse sections of the medullary pyramids taken at varying heights. Near the apices of the papillae but few cross-sections of the looped tubes of Henle are to be seen around the wide openings ofthe straight canals. But nearer the bases of the pyramids of Malpighi the small lumina of the former become more and more numerous. Again, while the open urini- ferous tubes are at first arranged close to one another, surrounded by circles of the orifices of the looped canals, Ave meet them further out- wards with larger intervals between them, which are occupied by cross-sections of the tubes of Henle in great numbers. But it is not only a difference in diameter Avhich distinguishes these two systems of uriniferous tubes from one another: the glandular epithelium in the open canals is of a species entirely distinct from that in the looped, and the so-called mem- brana propria presents several points of dif- ference, though of a less marked kind. The short trunks of the open canals have at their commencement no membrana propria; they are simply bounded by the fibrous frame- work of the apex of the papillae. Further on a delicate, transparent, limiting membrane be- gins to be apparent. This remains throughout the ramifications thin and fine, presenting always a single outline under the microscope. The case, hoAvever, is quite different wdth the looped canals (fig. 510, a, b, c). Here the membrana propria is stronger and thicker, and exhibits under high magnifying power a double contour. In the short primary trunks ofthe open canals we find an epithelial lining continuous wdth that covering the surfaces of the papillae. But the cells here are clearer, and of the Ioav columnar type, with broad bases turned towards the walls of the tube. A considerable lumen is still left, however, for the height of the cells is only 0*0300-0*0201 mm. They re- main thus as far as the branches of the first and second order (Henle). The last system of descending, and to those J Y Fig. 609. — Vertical section through a medullary pyra- mid of the pig's kidney (half diagrammatic), a, trunk of uriniferous tube opening on the tip of a pyramid ; b and c, branches of the same; d, looped tubes, or Henles canals; e, vascular loops; and /, branches of the rasa recta. branches Avhich run, as 518 MANUAL OF HISTOLOGY. we have seen, undivided for long distances towards the bases of the pyramids, possess a lining of gland cells only 0*0158 mm. high. The gland cell of the looped canals is, on the other hand, in the descending arms and curves, a very flat pavement element, presenting great similarity to the endothelium of the vascular system (§ 87). Its nucleus also, as in the latter, projects slightly beyond the surface (fig. 511, d). The resemblance to these vascular cells is really very striking. The recurrent tubes, however, of Henle's loops com- mence sooner or later to enlarge, and from this on the lining cells assume a different character. Instead of clear, flattened elements, the ordinary cubical gland- cells with distinct nuclei and granular protoplasm pre- sent themselves, with not unfrequently ill-defined boundaries between each one and its neighbour. Hence the recurrent arm becomes cloudy or granular in appearance, and its lumen decreases in diameter. These points are very well seen in fig. 511, Avhich is taken from the kidney of the infant. Here may be recognised, at a, the transverse sections of the open canals; at b, the clear, flat, epithelial cells of the descending tubes; and at c, the granular clouded gland elements of the recurrent arm of the looped uriniferous canals. We must, of course, expect to find the number of sections of tubes filled with dark gland-cells, increasing more and more as the cortex is approached. The clearest insight into the ar- rangement of parts, just described, is to be obtained from preparations in which the open canals have been injected from the ureter with one colour, and the blood-vessels of the medulla Avith another. Above, at the termination of the medullary substance and commence- ment of the cortex, the distinctive differences between the tAvo species of tubes disappear more and more, as far as diameter and epithelial lining are concerned. But even here injection from the ureter exhibits the peculiari- ties of the two systems; for, though the open canals are easily filled, the urine-secreting looped tubes remain, as a rule (unless special modes of treatment be adopted), completely devoid of the fluid injected. The upper portion of the medullary substance assumes, on injection of the blood-vessels, a deep red hue for a considerable depth. This is the boundary layer of Henle. Its deeper colour-is due to the presence of numerous tufts of radiating vessels. Fig. 510.—Looped canals from the renal pyramid of an infant, a, b, the two arms; c, another tube; tf, capillary blood- vessel. Fig. 511.—Transverse section through a renal pyramid of an infant, a, collecting tube with columnar epithelium; 6, descending arm of a looped canal with flat cells; c, recurrent arm with granular epithelial elements; d, transverse section of a blood-vessel; «, fibrous sustentacular tissue. ORGANS OF THE BODY. 5ig §271. Turning now to the cortical substance of the kidney, we find just as peculiar and complex an arrangement of parts as in that portion we have been considering. In vertical sections (fig. 512) Ave observe that it consists of tubes tAvist- Fig. 512.—Vertical section through the cortical portion ofthe kidney of the infant (half diagrammatic). A A, medullary processes; B, true cortical substance; a, collecting tube of the medullary pro- cess; b, finer tubes of the latter; c, convoluted tubes of the cor- tical substance; d, peripheral layer of the latter; e, an arterial twig; /, glomeruli; g, transition of uriniferous tube into one of Bowman's capsules; h, envelope of the kidney with its lymphatic interstices. ing and intertwining in all directions (B); but that, besides these, it is traversed from within outwards by cylindrical bundles (A) of about 0*2707-0*3158 mm. in diameter, at regular and short intervals. These bundles or cords are made up of canals of different calibre, Avhich, in some instances, become narrowed in their course outwards, where they are lost in convolutions immediately under the surface, forming there a narrow stratum of convoluted tubes (d). This cortical stratum of convo- luted elements, consequently, is interrupted at intervals by the bundles of straight uriniferous tubes (fig. 512, A), in about the same way that a board is pierced by groups of closely-standing nails driven through it. These bundles, although discovered long ago, have only very recently- received particular attention. They have been given by Henle the name of "pyramid processes," and by Ludwig that of "medullary radii." 34 520 MANUAL OF HISTOLOGY. We shall presently take into consideration their significance and bearing as regards the canals of the medullary substance. We may, if we like, look upon the mass of the con- voluted tubes, taken as a whole, as divided into a multitude of pyramidal blocks by these groups of straight passages,—the bases of the blocks being directed towards the sur- face of the organ. These may be named, as Henle has suggested, the "corti- cal pyramid*." Such a division, how- ever, is artificial, as a cut parallel with the surface of the kidney shows (fig. 513). Fig. 513.—Section parallel with the surface of the cortical por- tion of the kidney of an infant (half diagrammatic), a, transverse section of the uriniferous canals of tlie medullary processes or radii; 6, convoluted tubes of the true cortical substance; c, glomeruli and capsules of Bowman. Here we remark that the so-called cortical pyramids run into one another with the greater part of their lateral surfaces (b). Let us now turn to the con- sideration ofthe convoluted tubes of which the greater part of the cortical mass is composed. Those whose diameter is on an average about 0*0451 mm., un- dergo no farther division ; their outline is also single, and the membrana propria possesses con- siderable thickness, their outline being in almost every case smooth. The cells of the convoluted tubes are also very characteristic in appearance. Their bodies are made up of granular cloudy pro- toplasm, in which fatty molecules are often imbedded, increasing its opacity. In diameter they range between 0 0099 and 0*0201 mm. (ScIiweiggcr-SeideJ). Should the preparations have been treated by the method most generally in use at present, namely, that of maceration in hydrochloric acid, the convoluted tubes will probably appear dark, withoutany indication of alumen, ,. .. . . _ . and not unfrequently without any distinct marking off of one gland cell from the other. The mode of termination of the uriniferous tubes is a* point in regard Fig. 514.—From the cortical portion of the human kidney, a, arterial twig giving off the afferent blood-vessel (b) of the glomerulus (c», c>); c, efferent vessel of the latter; d, capsule of Bowman opening into a convoluted uriniferous tube of the cortex «. ORGANS OF THE BODY. 521 to which, at an earlier epoch, the most en-oneous views were held. They were supposed by some to end blind in the cortex, and by others to be continuous one with another by means of loops (Huschke, J. Muller). It was, to be sure, remarked that a peculiar congeries of vessels, known as the glomerulus of Malpighi was enveloped in a capsule, but its con- nection with the uriniferous tubes Avas denied in the most decided manner by the discoverer, J. Muller. In the year 1842, hoAvever, this connection was demonstrated by Bowman, who seems thus to have advanced the histology of the organ by several decades. Let us now turn for a moment to the mode of termination of the tubes in these capsules, knoAvn either in connection with Bowman's or J. Miiller's names. It is not unfrequently seen that, on arrival in the neighbourhood of the capsules, the uriniferous tubes (fig. 514) execute a series of very rapid undulations, more or less in one plane. Further, that immediately before opening into the capsule (d) there occurs pretty commonly a constriction on each tubule, more or less marked, and for a greater or less distance (fig. 515, d), and that the limiting membrane ofthe latter runs continu- ously into the apparently homogeneous tunic of the capsule. The latter has, as a rule, a diameter of about 0*1415-0*2256 mm., and spheroidal figure. It may, however, present itself of an elliptical or laterally Avidened form, or even heart-shaped. In a very thin superficial layer of the cortical substance, the cortex corticis of Hyrtl, neither capsules nor glomerules are to be found. They are, however, very numerous in the cortex. Their number, as estimated by Schweigger-Seidel, appears to be, in the kidney of the pig, about 6 to every cubic millimetre, or 500,000 for the Avhole cortical portion of the organ. It is generally held by many observers, among Avhom Bowman, Gerlach, and Koelliker may be mentioned, that those capsules situated deeper in the kidney are of greater magnitude than the others, and that those nearest the boundary, between the cortex and medulla, have the greatest diameter of all. The most difficult point to determine in regard to Bowman's capsules, is the relation to them of the vascular glomerulus and the cellular lining of the interior. It Avas at one time supposed that the vessels simply perforated the Avail of the capsule, and that the glomerulus lay naked Avithin the cavity of the latter. Other observers, as Koelliker, for instance, supported the vieAv as far as regarded the perforation, but believed the glomerulus to be covered over by the cells lining the capsule. Another theory is, that the knot of vessels is re- ceived into a depression in the capsule, somewhat in the same way as the lungs are received into the pleura. From my own investigations I am inclined to accept the last view as correct, besides which, it is easiest reconciled with the history of the development of the "Zt (Remak). It must, however, be admitted that the membrana Fig. 515.—From the kidney of the common snake (after Ecker). a, vas afferens; c glomerulus; 6, vas efferens; d, cessation of ciliated cells at the point of exit of the uriniferous tube e. 522 MANUAL OF HISTOLOGY. propria of the capsule is excessively thin over the glomerulus, ^and more like a homogeneous connective-substance or delicate boundary layer °f T^rnTn^our attention now particularly to the epithelial lining, we at once recognise the fact that the thick granular gland eel s of the convo- luted tubes become transformed, at the entrance to the capsule, into deli- cate pavement epithelial elements (fig. 515, e), Avhich line the whole internal surface of the capsule, and may be easily rendered visible by the aid of a solution of nitrate of silver (fig. 516, g). Among the lower vertebrates a number of ciliated cells are arranged around the entrance of the capsule, a most fragile species of ciliated epi- thelium (fig. 515, d). But the cellular layer said to exist over the glomerulus, is far more dif- ficult of recognition, and has not as yet been satisfactorily demonstrated. Nuclei are easily seen in this situation, but the borders of cells are not to be made out in the adult. From the fact that distinct cells are seen upon the glomerulus in the foetus, it has been supposed that they may have become fused together into one homogeneous nucleated membrane (Schweigger- Seidel). Other observers, on the other hand, have described here a complete covering of distinctly separate cells, and have even put forward statements in regard to their size as com- pared to the epithelial cells of the capsule. Our own experience inclines us to the belief that they are correct in their views (fig. 516,/). §272. From the preceding section we have learned that the convoluted tube is an important element of the cortex, and takes its origin from the capsule of the glomerulus. Leaving the destination of its other end for the present undecided, let us turn our attention in the meantime to thpse other constituents of the cortical portion of the organ whose position and coarser structure have been already touched on (§ 270); we allude to the pyramid processes or medullary radii. We may easily satisfy ourselves that, in these bundles of straight canals we have before us some of the open tubes of the medullary pyramids, which, after passing through the so-called boundary layer, arrive either singly, or, more rarely, in twos, in each of the processes, and traverse the latter from below upAvards, nearly to the surface of the kidney. These passages, remarkable for their considerable calibre (fig. 517, a), have received the appropriate name of collecting tubes (Ludwig). They are lined by transparent low columnar epithelium, which we have already seen in the last branches of the open medullary canals ; this is, hoAvever, less characteristic here than in the situation just alluded to. Fig. 516.—A glomerulus from the rabbit, a, vas afferens; 6, vas efferens; c, glomerulus; d, undermost portion of capsule without epi- thelium ; «, neck; /, epithelium of the glo- merulus ; and g, that of the internal surface ofthe capsule after treatment with nitrate of silver. ORGANS OF THE BODY. 523 passes °f ThP;eCOl!rtinS fi? * accomPanied ^ a number of smaller passages Ihese, as we shall see presently, are the descending anrl recurrent arms of the looped tubes of Henle, which are con^Ltly elements of the cortex both before and after'traversing the boZ^Z of fhe kidney ?"*" ^ ^ C°UeCting ***" °n ^ "^ at the SUrfaCe Fig. 617.—Vertical section from the kidney of the Guinea-pig (hydro- , chloric acid preparation), a, trunk of a collecting tube; 6, branches of the same; c, further subdivision; d, convoluted canal (intercalated portion); e, descending arm of a loop tube; /, loop; g, recurrent arm; and h, continuation as con- voluted uriniferous tube of the cortex. Fig. 518.—Tlie upper portion of a medul- lary ray from the kidney of the pig; a and d, so-called collecting tubes; b, their arched branches and continuation at c, into the descending arms of tlie looped canals. Maceration in acid (fig. 517) enables us to convince ourselves that on their arrival here they give off numerous branches, and eventually break up into arching, and, not unfrequently coded tubules (d). The latter may present in smaller animals a rugged appearance, not seen in larger creatures. These are the " intercalated portions " of Schweigger-Seidel or **** connecting canals " of Roth. 524 MANUAL OF HISTOLOGY. The same result is obtained when the passages of the gland have been e Fig. 519.—Vertical section from the kidney of the mole (hydrochlo- ric acid preparation), c, terminal branch of collecting tube ; d, por- tion of a convoluted uriniferous tube; e, descending arm of the looped canal; /, loop; g. h, re- current arm and continuation into a convoluted tube at i; i, neck of the latter; I, Bowman's capsule; m, glomerules. Fig. o20.—Diagram representing the course of the uriniferous tubes, based on the arrangement as seen in the kidney of the pig. a. Bowman's cap- sule; b, convoluted uriniferous tube; and c -e- current arm of loop; d, descending arm ; e con- voluted passages; /, collecting tubes joining to form one large, open uriniferous canal, a, whicli communicates with another canal, h; i, main trunk opening on the papilla. artificially injected through the ureter with success, as may be well ORGANS OF THE BODY. 525 in the dog and pig, for instance. In the latter animal the breaking up of the collecting tubes into arching ramifications (b) is easily recognisable. It appears, moreover, that loops of communication never occur between the ramifications of one collecting tube and those of another, although we might sometimes be easily led to believe otherwise in thick sections of injected kidneys. It was such deceptive appearances which tempted Henle, after he had been successful in filling the renal tubuli so far, through the ureters, to the conclusion that the terminations of the strait canals Avhich open at the apices of the papillae lay before him ; and farther, that a system of tubes, distinct from these open passages, and in no way communicating Avith them, is formed by the convoluted uriniferous canals, capsule of glomerulus, and looped tubuli of the medulla. Both modes of procedure mentioned above, namely, that of macera- tion in acid, and that of complete artificial injection, sIioav that series of passages, of various forms, spring from the arches just mentioned, and also earlier still from the collecting tube itself. These it is (fig. 518, c) Avhich, arriving in the medulla, somewhat decreased in size (fig. 517, h, g), form there the descending arms of the looped tubes of Henle (fig. 517, 519, e,f). Here, then, Ave have the origin of the descending portion of the loops. If Ave noAv folloAV it still farther—to repeat a former description—we find it (fig. 519, e) advancing into the medullary substance for a greater or less distance, and then curving round on itself (/), pursuing the same course back again to the medullary process (g, h). At the same time its diameter increases^ as already stated, and its lining of cells changes in character. Arrived here it turns off sideways, sooner or later, to become a convoluted tube of the renal cortex (i), terminating eventually as such in one of Bowman's capsules. We now have the Avhole intricate course of the uriniferous tubes before us. In some few instances Ave may be fortunate enough to succeed in driv- ing the injection fluid as far as the capsules. It seems almost superfluous to add another diagram (fig. 520) for the purpose of once more tracing the course Avhich the secretion must take from the glomerulus outwards. From Bowman's capsule (a) the fluid escapes into the convoluted tube (b), which, after numerous twists and curls in the cortex, arrives in the medullary substance, where it pur- sues a straight course (c). Lined by its own peculiar epithelium, it tra- verses the medullary pyramid in a direction more or less directly doAvn- wards, then forms a loop (c), and re- turns to the cortex (d). The recur- rent arm so formed alters sooner or later in character: it becomes wider and more tortuous (e), and, together with other similarly constituted tubes, empties itself into the collecting canal (/), which uniting with adja- cent passages of the same order at acute angles (g, h), pours out the urine finally at the apex of the papilla (i). Many efforts have been made 526 MANUAL OF HISTOLOGY. to ascertain the length of this very tortuous passage through whicli the urine must Aoav, and, from the calculations of Schweigger-Sei- del, it would appear that, from Bowman's capsule to the tip of the papilla is about 26 mm. in the Guinea pig, 35-40 in the cat, and about 52 mm. in man. Turning noAv to the susten- tacular substance of these very intricate glandular passages, we find that it consists of a small but by no means unvarying amount of fibrous stroma throughout tho whole organ. In the cortex it consists of par- titions composed of connective- tissue elements, with homoge- neous or streaky intercellular matter, which is somewhat more abundant in the neighbour- hood of the adventitial lamina of the larger blood-vessels and Bowman's capsules. At the surface of the organ, also, this stroma presents itself as loose areolar tissue, and is continuous here with the capsule of the kidney. The sustentacular sub- stance is somewhat firmer in the medullary rays than else- where. It appears to attain its highest degree of development, though this is always but of a very low order, in the medul- lary substance (fig. 521, e). It may be well seen in sections of kidneys hardened in alcohol or chromic acid, the sections hav- ing been well brushed out, and by the aid of maceration in hydrochloric acid the stellate connective-tissue cells may be isolated very clearly, as has been shown by Schweigger- Seidel. Fig. 522.—Plan of the circulation of the kidney (much shortened). 1. External portion of cortex. 2. Cortex 3. Boundary layer. 4. Medulla. 5. Apex of papilla! o, arterial twig; b, vein; c, vas afferens; d, vas efferens • e, vas efferens and /, capillary netwoi k of the surface; g, the vas efferens of a deeper-seated glomerulus; h, arteriola recta; i, venous radicle of the surface; k, capil- laries of the medullary process; ', of the convoluted tubes; m, venules rectoe; n, medullary capillaries; o network around the openings ofthe uriniferous tubes.' §273. We have now to consider the blood-vessels of the organ, which exhibit considerable pecidiarity of arrangement. As a rule both arterial and veinous trunks enter the human kidney at ORGANS OF THE BODY. 527 the hilus, having previously divided, after which their subdivision is con- tinued immediately within the organ. Here, after giving twigs to the fibrous envelope of the organ, they pierce the latter external to the infun- dibulum, each arterial twig be- ing usually accompanied by a large venous branch. In this Avay they advance be- tween the several medullary pyra- mids as far as the bases of the latter. At this point both kinds of vessels give off curving branches, forming imperfect arches among the arteries, but, on the other hand, complete anastomotic rings on the veins. From these arterial arches those branches spring whicli bear upon them the glomeruli of the cortical substance (fig. 522, a). They pass in general through the axial portion of those blocks of cortical tissue, bounded on either side by medullary processes (the cortical pyramids of Henle), giv- ing off towards the periphery the afferent vessels of the glomeruli (fig. 523, a, b; 512, e,f; 522, a, e). Each of these vasa afferentia subdivides at an acute angle within the glomerules of man and the mammalia (fig. 524, b, c1), and gives origin, after coiling and twist- ing there, to the vas efferens, by the union of the small branches so Fig. 523. Fig. 524.—Gomerulus from the pig's kidney. Fig. 525. formed (fig. 522, d; 526, d; 527). In the lower vertebrates, as for instance in the adder (fig. 525), the vas afferens (a) commences to curl 528 MANUAL OF HISTOLOGY. upon itself without undergoing division (e), leaving the capsule as an efferent vessel (b). In man and the mammalia this efferent vessel breaks up into a net- work of fine capillaries, with elongated meshes surrounding the straight uriniferous canals of the medullary radii (fig. 522, k ; 526, e). From the periphery of this netAvork a multitude of someAvhat wider tubes is given off (fig. 522,1; 526,/), which encircle with their rounded meshes the convoluted uriniferous tubes (/') of the cortical substance proper (or cortical pyramids (Stein, Key), and others). The most external layer of the cor- tex is destitute of Malpighian glome- ruli. It receives its capillaries (fig. 522, /) principally from the efferent vessels of the superficial glomeruli a (e), and to a smaller extent, and un- doubtedly in only some of the mam- malia, from certain terminal twigs of the arteries supplying the Malpighian bodies, Avhich pass forward directly to this layer of the cortex. Fig. 526.-From the kidney of the pig (half Immediately Underneath the Cap- diagrammatic), a, arterial twig; 6, afferent sule microscopic venous radicals may vessel of the glomerulus, c; d, vasefferens; . . -, v-\ • lt. r _p __ ti _l e, subdivision ofthe latter, forming the long- be recognised (l) in tfie IOrm Ot Stef late meshed network of the medullary processes; ficrnrpq (tfplhihp Vprhpiipn)i\ Otbpr /, round meshes of capillaries around the nguleb \Sieuuice veuieyenil). KJUiei convoluted tubes t; g, radicle of a venous venous tAvigs take their origin deeper in the cortical tissue (fig. 522, b), and both of these, joining usually to form larger trunks, empty themselves at the boundary betAveen cortex and medulla into the Arenous arches. Those long bundles of vessels Avhich appear in the medullary substance at its boundary, between the uriniferous tubes, running from thence doAvn- Avards, and either communicating Avith each other in loops, or forming a delicate network around the mouths of the uriniferous canals, at the apex of the papillfe, are knoAvn by the name of the .vasa recta (fig. 509, c, f, and 522, h, g, m). Between these, according to Ludwig and Zaicarykin, there is inter- posed another large meshed capillary network of finer tubes (n). This is a continuation of the oval netAvork Avhich encircled the straight urini- ferous tubes of the cortex. There still exists, hoAvever, great difference of opinion as regards the origin of the vasa recta. In our opinion they partake partly of the arterial, partly of the venous nature; but in many, though not the greater number of cases, more of the latter than of the former springing from the capillary network of the cortical substance Cficr. 527,/). ^ ° They are joined then by the vasa efferentia of the deeply-seated glome- ruli (fig. 522, g; 527, e, /, b), Avhich possibly constitute their most important source of supply. The number of arterial twigs, on the other hand, is quite inconsider- able as far as we have ourselves observed, which are given off from the branches bearing the glomerules, but before the latter are formed, and which sink as arteriolar rectse into the vascular portion of the medulla ffi" 522, A; 528,/). V °' As Ave have already remarked, the subdivision of stronger trunks to ORGANS OF THE BODY. 529 form these vasa recta gives rise in many instances to vascular tassels or bundles. m The confluence of the returning, straight venous vessels (fig. 522, m), takes place in a manner precisely similar. They commence partly as loops and partly as capillaries of the medulla. Others, too, spring from a special capillary network of larger tubes, situated at the apices of the papilla} (o). They empty themselves finally into tlie arching veins, already mentioned above, as lying at the boundary betAveen cortex and medulla. All earlier efforts to inject the lymphatics of the kidney, by the method of puncture, were unattended Avith success, and it Avas not until Ludwig and Zawarykin had invented a peculiar mode of procedure that it was effected. The kidney chosen to be operated on was that of the dog. The lymphatic canals of the parenchyma occupy the interstices of that areolar tissue which Ave knoAv to exist immediately under the capsule of the organ (fig. 512, i). Here they communicate externally with other ves- sels of the fibrous envelope, and penetrate internally through interstices in the connec- tive-tissue stroma, passing between the urini- ferous tubes and around the capsules of Bow- man and finer blood-vessels toAvards the deeper portion of the organ. But though in- tercommunication between the lymphatics of the cortex exists very freely, the fine absorbent vessels of the medullary processes can only be filled with some difficulty, and still later those of the medulla itself. The Avhole arrangement, indeed, resembles, to a great extent, that of the lymphatics of the male generative glands, the testes, to be referred to again beloAv. The canals collect- ing the lymph in the cortex take precisely the same course as the blood-vessels toAvards the hilus. They only commence to present valves in the vicinity of the latter, Avhere several very large trunks may be seen. The nerves of the kidney belonging to the sympathetic system, and springing from the plexus renalis, enter Avith the arteries of the organ. Their course and mode of termina- tion, as Avell as their relations to the pro- cesses of secretion, are hoAvever entirely un- known. The development of the organs, as investi- gated by Remak, takes place from the lowest part of the intestinal tube, in the form of holloAV buds, composed of a portion of the intes- Fig. 527.—A deepiy-seated glome- rulus, m, m, from the kidney of the horse, a, arterial twig; a /, vas afferens; m, glomerulus; e /, vas efferens of the latter, dividing at 6 into branches for the urini- ferous tubuli of the medullary sub- stance. Fig- 528.—From the boundary layer of the human kidney, a, arterial twig; e, branches of the same bearing at e and d, as vasa affe- rentia, two glomeruli; /, another branch (arteriola recta) breaking up into long capillary meshes of the medullary substance. 530 MANUAL OF HISTOLOGY. tinal germinal plate, with an external fibrous layer, consequently in the same manner as the lungs (§ 243). Subsequently the uriniferous tubes are developed from this system of cavities, in the form of solid bands of cells, which become hollow at a later stage of development, acquiring at the 'same time a membrana propria. The results of Kupffer's obser- vations, however, would seem to point to different conclusions. According to him'the organs in question are first developed in the form of saccules, on the passages of the primordial kidneys or Wolffian bodies. §274. From the investigations of Frerichs, it would appear that the kidney (whose sp. gr. is placed by Krause .and Fischer at 1 *044 for the medulla and 1*049 for the cortex) contains from 82 to 83*70 per cent, of water. Of the 18-16*30 per cent, of solid constituents, albumen seems to be the largest in amount. The proportion of fatty matter is from 0*1 to 0*63 per cent. The tissue of the organ is alkaline here also during life, and acid after death (Kiihne). As to the composition of the gland elements, we know that the membrana propria partakes of the nature of the elastic substances, Avhile the contents and whole substance of the cells must be looked upon as albuminous. The fatty molecules observed in the cell bodies explain the amount of adipose matter found in the organ, Avhich varies considerably. The decomposition products of the kidney found in its juices are of some interest. Among them appear inosite, hypoxanthin, xanthin, and at times leucin in considerable abundance (Staedeler). Further, in the dog kreatin is to be found (M. Hermann), in the ox, cystin and taurin (Cloetta). Most of these matters probably pass off in the urine. The urine is designed to carry off from the body the greater part of all the water received into it, as well as the principal products of the decom- position of histogenic substances, and also the excess of albuminous matters received into the system as food. Finally, it eliminates all mineral constituents set free in the interchange of material in the animal economy, together with any excess of salts which may be present in the alimentary matters. Taking all this into consideration, and especially that its composition is materially influenced by the nature of the alimentary matters, as far as quantity, wateriness, and chemical constituents are con- cerned, we can easily conceive that it must be subject to considerable variation even in normal states of the system, a variation which may become even more strongly marked under pathological conditions, or the influence of drugs which are partly eliminated through the kidneys. Healthy urine, freshly secreted, is a light yellow fluid of acid reaction, bitter taste, and peculiar odour. Its sp. gr. varies greatly, according to the proportion of water contained in it, and may range from 1 *005 to 1-030, but usually lies between 1*015 and T020. The amount of urine secreted in the course of the day varies also. It usually exceeds some- Avhat 1000 grammes, and may rise and fall between 1200 and 1800. On cooling a light cloud is generally found in animal urine, consisting of mucus secreted by the urinary passages, especially the bladder, together Avith the characteristic flattened epithelium of these parts, and a feAV mucous corpuscles. The acid reaction which human urine exhibits when just voided, de- pends not upon the presence of one or more free acids, for such are not tc be found in it, but upon acid salts, and especially on phosphate of sodium. ORGANS OF THE BODY. 531 The following are the principal constituents of urine, as far as the pre- sent state of science enables us to enumerate them with any certainty : urea, kreatin, and kreatinin, xanthin, and hypoxanthin, uric, hippuric^ and oxahc acids, extractives, colouring matters, indican, and salts. Grape sugar is probably also constantly present in the urine (Briicke), as well as oxalic acid (combined with lime), phenol, and taurol (Staedeler). The Avhole amount of solid ingredients varies much in the course of the day, ranging from 40 to 70 grammes. Urea (§ 28) is found in the large proportion of from 2*5 to 3 per cent. in normal urine, or to the amount of from 25 to 40 grammes per diem. This can, however, only be regarded as an approximate estimate. Its quantity is not increased by muscular exertion (Voit), contrary to an old and widely-spread theory. But under a diet consisting largely of animal food, it rises in amount ranging from 52 to 53 grammes, and after purely vegetable food or complete abstinence, its quantity becomes considerably diminished, and may only amount to about 15 grammes, or even less, per diem (Lehmann). Copious draughts of Avater and excretion of the latter through the kidney also increases its amount. Urea is the most important end product of the nitrogenous tissue elements, and consequently of the albuminous substances introduced into the system with the food. It appears in many cases to be derived from uric acid, a fact not only supported by the nature of its chemical constitution, but also by the observations of Wbhler, Frerichs, and Zabelin, that the injection of uric acid into the circulation increases the amount of urea excreted with the urine. Kreatin, however, has also been regarded as one of its sources. The introduction, also, of certain other bases into the body occasions likewise, it is believed, a rise in the quantity of urea eliminated. These are glycerin, guanin, and alloxantin. Uric acid (§ 25) presents itself, on the other hand, in far scantier amount than urea. In round numbers its proportion may be stated as about 0*1 per cent., and its quantity for the Avhole day from 0*5 to 0*9 grammes, descending even so Ioav as 0*2 grammes. Under similar con- ditions to those alluded to in discussing urea, its amount rises and falls analogously, though not, perhaps, to the same degree. It is contained in large quantities in the urine of the loAver order of mammals. It frequently presents itself in very large quantities during fevers, accompanied by great disturbance of the functions of respiration, a fact which lends additional support to the theory already alluded to, that the formation of uric acid is but a preliminary step to the formation of urea. As to where it is generated, we know as little as of urea. The products of its physio- logical decomposition are, besides urea, allantoin (§ 29), oxalic, and car- bonic acids. Strecker's discovery, also, that the decomposition of uric acid gives rise to glycin, promises farther light on this subject. Uric acid is supposed to exist in the urine in combination Avith soda, held in solu- tion by acid phosphoric acid. The sparing solubility of its salts is the cause of those sediments in the urine observed so frequently on the cooling of the latter in a saturated condition. The rose coloured or brick dust precipitates so formed consist of urate of sodium. The appearance, further, of one of the decomposition products of uri- acid in the urine is of great interest; this, oxalic acid occurs combined with ammonia (Schunk, Neubauer). Hippuric acid (§ 26) appears, under normal conditions, to occur in but small quantities in human urine, and to have a double origin. In the 532 MANUAL OF HISTOLOGY. first place, it possesses the nature of a decomposition product of the nitro- genous constituents of the body, which is indicated by the production of ben- zoic acid and oil of bitter almonds by the oxidation of albuminous matters. This source, however, is not its greatest, for, after a purely fleshy diet, its amount sinks to a minimum. In the next place, it takes its origin from vegetable food, which yields the unnitrogenous constituent of the acid. Consequently, its amount is much increased in man by a vegetable diet. It is also very abundant in the urine of the herbivora, while again, that of the calf is quite free from it so long as sucking (Wbhler). It has been already mentioned that benzoic acid, oil of bitter almonds, cinamic and kinic acids, and oil of tolu, when taken into the stomach, are eliminated by the kidneys as hippuric acid (§ 26). The nitrogenous part of hippuric acid, which, on combination with water, separates in the form of glycin (§33), is originally a product of the decomposition of the glutin-yielding tissues in all probability. We are not yet sure, hoAvever, in what way its construction takes place, or, in other words, how hippuric acid is generated. It was supposed, some years ago, that the process was carried on in the circulation of the liver (Kiihne and Hallwachs). It has been shown, on the other hand, more recently by Meissner and Shepard, that the acid is probably formed in the kidney itself exclusively. Oxalate of calcium, as already stated, is possibly constancy present in very smad quantity in normal urine; at all events, it appears very com- monly there. The frequent appearance of oxalic acid, also, coincidently Avith the decomposition of uric acid, is a point of some interest (p. 35). Kreatin may likewise play a part here. Of one point, hoAvever, Ave are certain, that oxalic acid may take its origin from vegetable ali- ment. Carbolic and taurylic acids (p. 36) are also possibly constant con- stituents of human urine (Staedeler). We now come to two substances with all the characters of decomposi- tion products of nitrogenous tissues, namely, of muscle and nervous matter; we allude to kreatin and kreatinin (§ 30). The latter is always to be found in human urine (Neubauer, Munk), in which kreatin may also be present. Both bases are almost invariably to be met with in the urine of dogs (Voit, Meissner). In considering this subject, sufficient weight must be given to the fact that kreatin is converted into kreatinin by the action of acids, whilst the latter may be transformed into the former by contact with alkaline solutions. Their presence, then, in acid or alkaline urine must be judged accordingly. The amount of these two substances increases greatly under an abundantly fleshy diet. Injected also into the blood they are eliminated with the urine (Meissner). In starving animals, likewise, in which combustion of their own muscular tissue is going on, the quantity of both alkaloids is found to rise (Voit, Meissner). Muscular exertion, on the contrary, produces no effect on their generation. It is an interesting fact, that the urine of dogs whose ureters have been ligatured, and which has consequently been secreted under high pressure, contains no urea, but an abundance of kreatin (M. Hermann). Xanthin and hypoxanthin are likewise present in minute quantity in human urine. The first is also to be found in the renal secretion of do"s after moderate muscular exertion (Meissner). As regards the existence of grape sugar as a normal constituent of urine ORGANS OF THE BODY. 533 Avhich is maintained by Briicke and denied by others, no definite con- clusions can be come to upon the point. The extractive matters of the urine are partly derived from the products of mutative processes in the tissues of the body, and partly from the alimentary substances introduced into the latter. Their daily amount varies from 8 to 20 grammes and upAvards. From Lehmann's researches it Avould appear that they are most abundant after vegetable food, and appear in small amount under a meat diet. We have already referred to the unsatisfactory state of our acquaint- ance Avith the colouring matters of the urine (§ 36). It is a point of interest, however, that indican and indigo-chromogen have been proved to exist here by Lloppe and Jaffe working on Sclienck's and Carter's method (§ 36). This explains the fact that blue crystals of indigo (uroglaucin) may be obtained by treating urine with the mineral acids, and that these crystals are found at times in the latter. Indigo-carmine has also been met Avith here. From the circumstance that indican is not present in the rest of the body according to Hoppe's investigations, and that it is found in the urine of the lower mammals as well, Ave may conclude that it is generated by the kidney. The mineral matters of the urine are, owing to the nature of the fluid, very variable in their amount. The latter may be set down at from 10 to 25 grammes for the twenty-four hours. They consist of chlorides of the alkalies, and indeed almost entirely of compounds of soda, especially of chloride of sodium, Avhich is present in from 1 to 1*5 per cent., amounting in the day, on an average, according to Bischoff, to 14*73 grammes, but falling sometimes as low as 8*64, or rising again as high as 24*84 grammes. Chloride of sodium, which is introduced, as is well known, into the system with the food, is a constant constituent of the body. Both the perspiratory glands and kidneys take part in its elimination. There are many points of interest attached to this process. If the blood and tissues of the body be saturated with chloride of sodium, all the absorbed salt is again excreted by the organs mentioned. If, on the other hand, the body have previously suffered a deprivation of the salt- excretion does not follow upon its ingestion, until the system has recovered its normal percentage of chloride of sodium. If, however, all supply of the latter be cut off, as is the case in starvation or existence on food devoid of saline ingredients, it still continues to be eliminated, but in much smaller and ever decreasing quantity (Voit), until, after some days, albumen begins to make its appearance in the urine (Wundt)—a proof of incipient disin- tegration of the blood. The amount of chloride of potassium and ammonium in the urine is small on the other hand. Urine contains, farther, certain phosphatic salts, and especially acid phosphate of sodium with phosphate of calcium and magnesium. As is Avell known, the corresponding combination of potash (§ 170) is to be found in muscle, Avhile the phosphates of the earths are combined with some of the histogenic substances, and especially albumen. The brain likeAvise contains phosphorus as one of the ingredients of lecithin. According to the nature of the alimentary matters, phosphoric acid appears in greater or less abundance. It does not, however, fail to be excreted Avhen the system ceases to be supplied with it (Bischoff). The amount daily eliminated by the kidneys has been estimated by Breed at from 3*8 to 5*2 grammes. Its rise and fall is to a certain extent 534 MANUAL OF HISTOLOGY. proportional to that of urea, Avhich likeAvise originates in the splitting up of some of the albuminates. Among the urinary salts we also find sulphates of the alkalies, amount- ing in the day to 2*09 4 grammes (Vogel). These are augmented by animal food, and diminished, on the other hand, by vegetable diet (Lehmann). From the fact that, as a rule, no sulphates are introduced into the body Avith the food, those which appear in the urine must be looked upon as developed in the decomposition of histogenic substances having sulphur as an ingredient. This latter element is also cast out of the economy as a component of taurin, as well as of those particles of horny tissue con- stantly being shed from the surfaces of the body. The secretion of the kidney possesses likewise traces of iron and silicates, and small quantities of ammonia; further, nitrogen and carbonic acid gas, both free and in combination, together with a trace of oxygen. Among the abnormal and occasional constituents of urine, Ave^ have (without taking into account casual matters) albumen in many diseases and disturbances of the circulation. Then again, haemoglobin, as, for instance, after poisoning with phosphorus or injection of biliary acids into the blood, causing destruction of the red corpuscles of the same. Grope sugar is found in diabetes, and inosite likewise, as also in Bright's disease. Lactic acid, too, is frequently to be found in normal urine and after acid fermentation. Besides these fatty matters, butyric, succinic, benzoic, and biliary acids (§ 27), present themselves here; also the pigmentary matters of the bile (§ 37), cystin (partly in solution and partly in crystalline concretions), leucin, and tyrosin (in various diseases). AUantoin, likeAvise (§ 29), a product of the artificial decomposition of uric acid, which occurs also in the liquor amnii of ruminants and urine of sucking calves, was met with by Frerichs and Staedeler in the urine of dogs suffering from obstructions to respiration. It was found also by Meissncr in abundance after fleshy food or injection into the circulation of kreatin. Cats fed in the same way excrete it also. According to an old and, we believe, correct view, urine, when exposed for several days to the air, undergoes a process of acid fermentation, by which, as has just been observed, lactic and acetic acids are produced, increasing its acid reaction, and during which crystals of free uric acid, coloured by the pigments of the urine, are deposited. This view, however, is stated by some later observers to be incorrect. According to them, the acid reaction of the urine becomes less marked the longer it stands, the acid phosphate of sodium is converted into a neutral combination, and acid urates and free uric acid are produced. The latter are then throAvn down (§ 25). Later on, another, an alkaline fermentation, is frequently observed, in which urea is split into carbonic acid and ammonia (§ 28)". Coincident Avith this, the urine becomes someAvhat decolorised, extremely foetid and turbid, and deposits a whitish sediment, Avhile a light pellicle forms upon its surface. The former consists of crystals of ammoniaco-magnesian phosphate (§ 42), and of urate of ammonium (§ 25). This process of alkaline fermentation may take place, on the other hand, almost immediately after the urine has been voided, or even during its sojourn in the bladder. § 275. We noAv come to the question, how far the secretion of urine is to be ORGANS OF THE BODY. 535 regarded as merely consisting in an elimination of matters from the blood which already existed there ? From the fact that some of the most important and best known con- stituents of the urine had been met Avith in this central fluid (§ 75), the agent in so many of the exchanges of matter going on in the system, it was for a long time supposed that the secretion of the fluid in question Avas analogous to the process of filtration, and so essentially dissimilar to the formation of bile in the liver. But though the statements of Zalesky. that urea and uric acid are generated by the kidneys, have been shown to be incorrect, still many circumstances point to caution as regards the acceptance of this old vieAv. Thus, for instance, the acid nature of the urine, the transformation of benzoic into hippuric acid in the kidney itself (Meissner and Shepard), and the fact that albumen does not transude under ordinary circumstances. It seems extremely probable, indeed, that the process of excretion of urine partakes both of the nature of secretion and filtration. When Ave consider the structure of the. kidney, as described above, the question also naturally presents itself—Which of the two vascular apparatuses, the glomerulus or the network investing the uriniferous tubes, presides over the excretion of the fluid 1 When Ave remember that the kidney and glomerulus go hand and hand among the vertebrates, we must be inclined to ascribe to this portion of the vascular system the greatest importance, even though the gland cells of the convoluted tubes do possess the poAver of secretion, and represent something more than a mere passive epithelial lining, which is hardly to be doubted. It is only the straight canals running from the external surface of the medullary rays to the points of the papillae, Avhich present the latter in our opinion. If we bear in mind that in man and in the mammalia the vas afferens breaks up into branches in the glomerulus, besides being arranged in con- volutions, and that these branches combine again to form a smaller vas efferens,—that a retardation of the blood must be brought about in the convolutions of the glomerulus, owing to the greater area to be traversed by it, will be clear; and that this sluggishness must be succeeded by rapid circulation in the narrow efferent vessel, giving way again to a second and more clearly marked retardation in the capillary network around the uriniferous tubes, is also plain. This narrowness of the vas efferens produces, then, a greater or less degree of obstruction to the blood in the glomerulus, and, consequently, to an increase of lateral pressure, far exceeding that of the second capillary system ; it favours thus excre- tion. The blood in the capillary network, on the other hand, investing the uriniferous tube, Aoavs certainly under smaller pressure, and appears partly to possess the poAver of absorption, and to rob the urine as it passes of some of its water again (Ludwig). The peculiar disposal, further, of the derivatives of the vas efferens, first around the passages of the medullary ray, and subsequently around the convoluted tubes of the cortex, seems to indicate some physiological purpose beside all this. The progress of the urine towards the openings on the papdke takes place without any muscular aid, merely through the vis a tergo produced by the continuous secretion behind pushing forward the columns of fluid in the uriniferous tubes. Besides this, in the ureters the gravitation towards the bladder comes in aided by the contraction of the muscular walls of the ureter (Engelmann). Owing to the well-known anatomical arrange- 35 536 MANUAL OF HISTOLOGY. ment of parts below, a return of the urine from the bladder into the ureters is just as difficult as from the latter into the papillae. § 276. The urinary passages commence in the calyces renales at the pelvis of the or<*an. In these parts we find an external fibrous tunic, a middle layer of smooth muscular fibres crossing each other in various directions, and but slightly developed in the calyces, and then an internal mucous membrane with a smooth surface and laminated epithelium of peculiar flattened cells, to which Ave have already referred (p. 141). Here Ave also meet with either tubular or racemose mucous glands in man and the larger mammals. They are not so frequently seen in man as in other animals, as, for instance, in the horse. The ureter presents the same structure, except that its muscular tunic is stronger, consisting of an external longitudinal and internal circular layer of fibres, to which is added, loAver doAvn, a third and most internal layer of longitudinal elements. Under the epithelial lining the blood- vessels are arranged in a dense network of delicate tubes. In the fibrous covering of the ureter in the rabbit a nervous plexus, almost destitute of ganglion cells, is to be found. The mode of termination of the nerves is not yet known. As is Avell known, the ureters terminate in a round diverticulum known as the bladder or vesica urinaria, piercing its walls obliquely. The structure of the bladder is similar to that of the ureters. Its external surface is in part covered by a serous membrane, the peritoneum. Its muscular coats, however, attain a much greater degree of strength here than in the ureter, and are no longer arranged Avith the same regularity, consisting for the most part of obliquely running muscular bundles, interlacing in a retiform manner. At the neck of the organ these fibres are disposed in a thick circular fasciculus, the spit incter vesicae, besides Avhich they form, externally, on the anterior wall and summit, longitudinal masses, to which the term detrusor urinae is applied. However, much variety is to be observed in the arrangement of the muscular tissue. Within the organ the mucous mem- brane presents a smooth surface and characteristic flattened epithelium. A feAV scattered mucous glands of small size may be fouud in the fundus and around the neck. Here also a complicated network of capillaries lies close under the epithelium. The manner in Avhich the nerves of the bladder ter- minate is just as obscure as in the ureters. The female urethra is lined by a mucous membrane thrown into heavy longitudinal folds and covered with papillae. It is studded also, in the neighbourhood of the bladder, Avith a number of mucous glands of either simple or complex structure, the largest of Avhich are known by the name of glands of Littre. The muscular substance of the part, Avhich is of con- siderable thickness, consists of separate longitudinal and oblique bundles of fibres ; the epithelium is of the flattened species. The vascularity of the Avails is very considerable, the vessels having a plexiform arrangement. 5. The Generative Apparatus. § 277. The generative apparatus of the female consists of the ovaries, the Fallopian tubes, opening into a diverticulum called the uterus, the vagina, and external genital organs. Finally, the mammary gland is connected with the reproductive functions of the female. ORGANS OF THE BODY. 537 The ovary (fig. 529), the most important part of the whole, is a very remarkable organ. It may be divided into two portions, namely, into a kind of medullarii substance, i.e., non-glandular and very vascular connective- tissue, and into a glandular parenchyma enveloping the latter. The first has been named the vascular, the external layer the parenchymal zone by Wal- deyer. Taking the former of these first, we find it commencing at the so-called hilus ofthe organ (the hilus stroma of His), at Avhich spot large blood and lymphatic vessels enter and leave the part. Traversed in all directions by innumerable blood-vessels, this fibrous nuc- leus presents itself as a spongy red mass, comparable to cavernous tissue. From it a number of centrifugal bands of fibrous tissue are sent off into the gland parenchyma, where they form septa, and coalesce again peri- pherally, giving rise, by their close intermixture, to an external boundary layer (fig. 530, b). It was formerly held that this last might be divided Fig. 529.—The ovary, a, stroma; b, mature Graafian fol- licle; c, a larger one; d, a fresh corpus luteum with thick lining*; e, an old corpus luteum; g, veins with their first branches, /, within the organ. Fig 530.—Ovary ofthe rabbit, a, germinal epithelium (supposed serosa); b, cortical or external fibrous layer; c, youngest follicles; d, a somewhat better developed and older one. into an internal lamina of very dense texture, the albuginea, and an external serous membrane covering the latter. This condition of parts does not exist, however. The surface of the ovary uncovered by peri- toneum is coated with a layer of low columnar cells (a) (Pfiiiger, Wal- deyer). To this the suitable name of germinal epithelium has been given. 538 MANUAL OF HISTOLOGY. Having now dwelt for a moment on the general anatomy of the ovary, let us commence a more particular consideration of its finer structure with that of the glandular portion. Immediately underneath the boundary layer just mentioned is situated a remarkable stratum, almost quite destitute of vessels, Avhich has only recently been recognised. This, Avhich is composed of glandular consti- tuents in process of development, may be called the cortical zone or zone of the primordial follicles. Here the essential elements of the organ lie closely crowded in several layers, namely, the young ova (c, d),—beautiful globular structures about 0*0587 mm. in diameter, consisting of naked granular protoplasm con- taining fatty molecules and a spherical nucleus of about 0*0226 mm. in diameter (fig. 531, 1). Each egg-cell, further, is enveloped in a mantle of small nucleated ele- ments. The narroAv interposed septa which exist here, forming the stroma of the ovary, are composed of closely-packed fusiform connective-tissue cells, and generally surround each ovum, including its covering of small elements, Avith a species of special tunic, bounded towards the ovum by a homoge- neous limiting layer or membrana propria. This then constitutes the so-called follicle of the ovary in its earlier form. In this description we have followed the appearances presented in the ovary of the rabbit; but in the organs of other animals, as, for instance, the dog and cat, a more or less race- mose grouping of the egg-cells is met with fre- quently (fig. 536, c), (Waldeyer). In man and the larger mammals the connective fibrous tissue is more abundant, and the ova more distant one from the other. Turning uoav from this external stratum, with its enormous number of germinal structures, to the more internal portion of the ovary, wo find the follicles as we proceed more and more highly deve- loped. Here we encounter some Avhich may have even attained a diameter of 00902 or 0*1805 mm. The ovum contained Avithin them is also increased in size, and is enveloped in a distinct membrane (2). The minute cells, situated within the latter and around the ovum, are also present, but in several layers now, Avhile a system of capillaries may also be observed encircling the follicle with a small number of vessels. In other larger follicles (fig. 530, d), the layers of the smaller elements just mentioned begin to separate from one another, producing a narrow inter- space between the two. In the subsequent growth of the follicle this becomes larger and larger, filling at the same time Avith a watery fluid. A follicle at this stage may measure from about 0*3835 to 0*4512 mm. in diameter. On the internal surface of its walls, now supplied by a well- developed capillary netAvork, may be noticed at some one point an enlarged ovum increased to 0*1805 mm. transverse measurement, containing within it a nuclear vesicle of 0*0609 mm. and nucleolus of 0*0135. The touch capsule of the cell is also increased in thickness to 0*0063 mm., and the Avhole ovum is enclosed within a mass of small cells arranged in layers Fig. 531.—Early follicle from the ovary of a rabbit, In 1, the ovum is seen with- out the zona pellucida, a; in 2, the latter begins to be apparent. ORGANS OF THE BODY. 539 which cover also, peripherally, the whole internal surface of the follicle as an epithelial lining. Finally, the ovarium (fig. 529) generally contains a limited number of mature follicles, varying from 12 to 20, Avhich, from the fact of their having been discovered at the end of the seventeenth century by an ana- tomist of the name of De Graaf, have received the name of the Graafian follicles. These vary in diameter, according to the maturity and size of the animal, from 1 to 8 mm. (b, c). Fig. 532 represents such a follicle with its Avail (d, e), its epithelial lining (c), the ovum (a) embedded in the thick epithelial mass (b), and enlarged cavity. In the walls of the follicle, or, as it has been named, the theca or mem- brana folliculi, two laminae may be distinguished, an internal and external. Within the first of these the "ramifications of the capillaries take place, Avhile the external contains the branches (e) of the larger vessels. The outer layer is composed of the same elements as the remaining sustenta- cular matter of the organ, namely, of fibres of connective-tissue and very densely crowded fusiform cells. Owing to the fact that the blood and lymphatic vessels of the tissue form around the external layer of the membrana folliculi a series of open sinuous cavities, the follicle may be separated with ease, and in a perfectly uninjured condition, from its surroundings. In the internal lamina of the wall Ave then observe that the capillaries enter the latter in lines con- ■ 532.—Mature follicle, a, ovum; 6, layer of epithelium enveloping the latter and lining '' the cavity of the follicle c; d, fibrous wall; e, external surface of the foUicle. verging towards the centre of the follicle, forming internally a very dense network with circular meshes. Like embryonic tissue this layer is parti- cularly rich in cells of different forms and dimensions. Besides smaller ones resembling lymphoid elements, we find another kind of larger cells, roundish or polygonal in figure, and measuring about 0*0226 mm. m diameter These are, in part, situated in the intervals between the vessels, 540 MANUAL OF HISTOLOGY. and partly around the latter, enveloping them in a manner Avhich reminds one of the mode of formation of the Avails of vessels already described (§211), (His). The Graafian follicle is distended by that fluid, the commencement of whose formation Ave have already alluded to above. It is transparent, alkaline in reaction, and contains albumen. It is known as the liquor folliculi. The round nucleated cells covering the internal surface of the cavity, in ill-defined layers, are known, taken as a Avhole, as the formatio or membrana granulosa: the elements measure individually about from 00074 to 0*0113 mm. The breaking down or solution of the latter may account for the presence of albumen in the fluid. The point at which this stratum attains its greatest depth, in order completely to surround the egg (cumulus proligerus of embryologists, cumulus ovigerus of Koelliker), was formerly supposed to be at that aspect of the follicle nearest to the periphery of the organ. More accurate and recent observation has, how- ever, shown this view to be erroneous, and that the ovule is attacned to that side of the follicular cavity, as a rule, which is most remote from the surface of the ovary (Schrbn., His). It may, hoAvever, be found in the first position ( Waldeyer). The mature ovum (fig. 533, 1, 2) is still of great minuteness, and therefore not easy to find. In order the better to investigate its nature Aye are obliged, in the first instance, to free it from the elongated cells of the membrana granulosa, fixed upon it in a radiating manner (2, c). It is then found to be a spherical structure from 0*28 to 0*1379 mm. in diameter, or, in other words, a beautifully developed cell with a thickened capsule. All these different parts have received names from the anato- mists of former times. The capsule, in the first place, is knoivn as the zona pellucida or chorion. It presents itself as a soft, transparent, semi-solid substance, homogeneous in appearance, in all probability pierced, nevertheless, by minute pores (fig. 73, p. 83). It is now about 00090-0*0113 mm. in thickness. Its origin is at present unknoAvn. It may either be formed by the ovum itself, or deposited upon the latter from without. The latter, in our opinion, is the most plausible hypothesis. Chemically it is a substance difficult of solution in alkalies, resembling elastin in a great measure. The cell body (b), possessing a hardened cortical layer, appears in man and the mammalia as a more or less opaque mass, containing in a viscid substratum molecules of coagulated albuminous matters, as well as granules and globules of fatty substances. It is known as the vitellus. The nucleus (1, c), generally known under the name of the vesicula germinativa, or germinal vesicle of Purkinje, is situated in the mature ovum excentrically. It is a very delicate and perfectly spherical vesicle of 0*037-0*0451 mm. in diameter, quite transparent, and presents -i round and highly refracting nucleolus*^), from 0*0046 to 0*0068 mm in diameter. The latter has received the name of the macula germinativa or germinal spot of Wagner. Let us noAv turn to the blood and lymphatic vessels of the ovary We have already been obliged to refer to the blood-vessels in the fore- going description. They arrive at the hilus in the form of larcre arterial and venous twigs, the former taking a very tortuous spiral course on their way thither. Arrived in the stroma they break up into numerous branches, so that the medullary substance of the latter is in reality a ORGANS OF THE BODY. 541 mass of vessels. The interstitial tissue is extremely scanty, consisting merely of intersecting, bands of fusiform ceUs, which turn off from the middle muscular tunic of the arteries. Intimately united to this interstitial substance are to be found the venous walls which gape on being cut through, hor this reason the whole tissue of this so-called hilus stroma has been regarded as composed of the modified walls of vessels, themselves traversed again by smaller vessels (His), recalling to mind the structure of the corpora cavernosa (Rouget). From this it Avould appear that the spindle cells of the medullary substance are muscular elements (§ 163, p. 283), in keeping with Avhich view the fresh stroma of the ovary has been observed to possess the power of contractility by both His and myself. Further, numerous pencils of vessels are seen to penetrate from the periphery of the stroma of the hilus between the internal follicles towards the surface of the organ. In this course they supply follicles, as mentioned above, with a dense network of vessels. Prolongations of the latter, hoAvever, penetrate still further towards the zone of cortical cells, doubling on themselves, for the greater part, before their arrival in the latter, Avhich remains almost entirely devoid of vascularity. But besides being very rich in blood- vessels, the Avhole stroma of the hilus possesses numerous lymphatics. In the latter, which are similar in their arrange- ment to the veins, the characteristic vas- cular cells of these passages may be every- where rendered visible by treatment Avith nitrate of silver. Their relation to the follicles is of special interest, however. The latter having attained a large size, and having pressed forAvards towards the sur- face, may be seen in this position to be surrounded by a dense network of lymphatics, situated principally in the external lamina of the Avail of the follicle. According to His the apex of the latter is completely destitute of lymphatics, as also of blood-vessels. Smaller follicles also, as soon as their internal tunic has been developed, are found to present an investing network of lymph canals, even long before they have reached the surface of the organ. The numerous nerves of the ovary springing, for the most part, from the genital ganglia, as has been shown by Frankenhaiiser (§ 279), contain medullated and non-medullated fibres, and enter the organ with the arteries. Their ultimate distribution is still obscure. Lying betAveen the ovaries and Fallopian tubes a trace of the Wolffian bodies may be seen on either side of the uterus, in the form of a feAv small tortuous canals, situated in the ala vesperiilionum. To this the name of the parovarium has been given. The tubules are composed ol a fibrous Avail, epithelial lining, and transparent contents. The chemical composition of the ovary still awaits accurate investiga- Fig. 533.—Egg of a mammal, 1, one in which a rent has been made in the zona pellucida (a), allowing the escape (6*) of a portion of the yelk, b*: c, the pre- germinal vesicle with germinal spot, d; '1, mature ovum covered with radiating epithelial cells, c; with the chorion, a; and yelk, b. 542. MANUAL OF HISTOLOGY. tion. Its sp. gr. in the human female is, according to Krause and Fischer, 1-045. Chemical analysis, on the other hand, of the ova of the mam- malia is not practicable, owing to the minuteness of the objects to be dealt with. Remarks.—See Waldeyer's beautiful monograph, "Eierstock und Ei," Leipzig, 1870. The best work which has, up to the present, appeared on the subject. §278. Having in the foregoing section become acquainted Avith the structure of the ovary, let us now take up the question, Whence are the follicles with their cellular contents, and especially the ovum ? For an answer to this query we shall be obliged to folloAv up the development of the organ. The following is the view Avhich obtains most generally in regard to the origin of the ovary. The germ-preparing glands of the female spring from the sides of those temporary urinary glands of the embryo knoAvn as the Wolffian bodies. The epithelial covering of the Wolffian bodies is observed very early to undergo a thickening at the spot in question in the embryonic chicken ( Waldeyer). At the same time a small cellular groAvth makes its appear- ance here also, springing and projecting from the connective-tissue mass of the organ. Noav, from the thickened epithelium covering this projection the rudi- ments of the Graffian follicles and ova are formed, as well as the later ovarial epithelium, while from the connective-tissue the vascular susten- tacular substance of the organ takes its rise. The epithelial clothing is soon observed to contain (not only in the chick, but also in the mammal embryo) certain enlarged cells or primor- dial ova. The further changes consist in an intermixture of the fibrous and epi-4 tbelial constituents. Fig. 534 gives a representation of what now takes Fig. 534.—Vertical section of the ovary of a human foetus 32 weeks old (after Walaejier) a germinal epithelium; 6, younger egg-cells, the "primordial ova" contained in this- c in- growing band of fibrous connective-tissue; rf, epithelial cells in process of being Voided in; «, youngest follicles; /, ova and germinal epithelial cells in groups; g, lymphoid cells place. The connective-tissue processes increasing rapidly in leii"th the aggregations of cells become smaller and smaller, and contain one or ORGANS OF THE BODY. 543 several primordial ova. In this way follicles are eventually formed in their most rudimentary form. On the externa] side of the Wolffian body this epithelium dips down to form a groove. From this, again, a canal is formed subsequently, the canal ot Muller (Waldeyer), and from it the Fallopian tube and uterus are developed. Several very important points have recently been brought forward by Pfiiiger in regard to the follicles, which enable us the better to com- prehend some statements made long ago by Valentin and Billroth, which had almost sunk into oblivion. These have since been confirmed by many other observers, among whom may be named Borsenkorp and Spiegel- berg, Llis, Letzerich, Langhanns, Frey, Koelliker, and Waldeyer. According to Pfiiiger's investiga- tions the Graafian follicles are secondary formations. He asserts that they take their origin from ob- long or irregular aggregations of cells by a process of constriction affect- ing the latter at various points. To these collections of cells the name of primordial rudimentary follicles, or, more briefly expressed, " ova chains" (Eistrangen), has been given (fig. 535). They contain besides peripheral cells of small size and pale colour (the elements of the future membrana granulosa), the primordial ova. These are situated in the axis of the group, and may be distinguished by their greater magnitude and granular protoplasm. Their existence, therefore, anterior to the formation of the follicle, is a point about Avhich there can be but little doubt. These cell-groupings are sometimes enclosed in a homo- geneous membrana propria, giving rise to regular tubular structures, as in the cat. This may be absent in other cases, as in the calf. The arrange- ment of newly-formed follicles which, instead of occurring singly, appear still in groups, or ranged like beads on a string (Follikelketten), is thus easily understood as regards the mode of their development. The primor- dial ovum possesses farther vital contractility, and multiplies by segmen- tation (Pfiiiger). It is only at certain points, however, that at this period we come upon these " ova chains," whicli explains the fact of their having so long remained undiscovered. . Pfiiiger states that he has satisfied himself that in the kitten, four weeks after birth, the period for finding these primordial tubes is already passed. But towards the time of casting their young the formative energy awakes afresh in the ovary of the mammal, and not only are Fig. 535.—Chains of follicles from the ovary of a calf. 1, containing ova in process of develop- ment; and, 2, showing gemmation to form Graaffian follicles. 544 MANUAL OF HISTOLOGY. there formed both ova and Graafian follicles, but the manner m which^the process is carried on is the same as before,-" ova chains appear anew. The origin of these remarkable structures is a question of great interest. Pfiuger was the first to point out that they were probably derived from in-growth of the epithelium on the surface of the ovary, in the form of tap root like processes, and Waldeyer has since proved his supposition to be correct. • „ ..^ ■,, . j- In suitable preparations (fig. 536) it is a matter of no difficulty to dis- tinguish the growth downwards into the connective-tissue sustentacular tissue beneath of the germinal epithelium at certain points (b). In Fig 53G. the middle of such cellular masses certain large elements or primordial ova are to be seen (c). Then by constriction at the surface of the organ the follicle chain, or ova chain, represented in fig. 535, is produced. Thus, then, is the ovum formed. But what becomes ofthe ova1? Their destiny is twofold,—one during the period of immaturity of the animal, another all through the period of generative activity. In the first period it Avould appear that both follicle epithelium and ovum are frequently destroyed by fatty degeneration (Slavjansky). In very young and healthy mammals, moreover, I myself have not unfre- quently observed an extensive colloid metamorphosis of the whole con- tents of the follicles. But the destiny of the ovum is quite different in the mature animal. Here containing the material for the construction of a neAv individual, it is destined "to become free by bursting of the Graafian follicle. It was formerly believed that the stimulus of connection with the male Avas requisite, as a rule, to bring about this rupture. Hence those Avho held this view regarded the Graafian vesicles as persistent structures, of which only a certain limited number ever really did burst during the reproductive period of female existence. Recent investigation, hoAvever, has thrown quite a new light on this subject. We now knoAv that the expulsion of an ovum takes place with every menstruation in the human female. It is, therefore, independent of sexual intercourse, since this occurs in virgins as well as in married Avomen. Amongst the lower animals the period of heat, or rutting, is that in which either one or more ova are liberated. ORGANS OF THE BODY. 545 When a Graafian vesicle arrives at this epoch of its existence it under- goes a further increase in size, owing to continuous proliferation of the cells of the internal membrane of the follicle and accumulation of fluid ■within it. It now gives rise to a prominence on the surface ofthe ovary, from the fact of its being tense and swollen, and no longer situated in the stroma of the organ, but merely covered by a thin laver of connective- tissue. Finally, there comes a moment at which the Avail of the follicle becomes so stretched and distended that it must succumb to the forces acting on it, and it ruptures. The rent always takes place at the point of least resist- ance, and consequently in the external surface of the ovary, which is only covered by a thin fibrous envelope. For the reception of the ovum at this time the ostium abdominale of the Fallopian tube is closely applied to the surface of the ovary. The ovum noAv commences its journey down the tube toAvards the uterus, in which it arrives after some days. After it has escaped from the Graafian follicle, the inherent energies of the encapsuled cell are aroused by the penetration of spermatozoa into its yolk, and the process of segmentation commences (fig. 537, 1), which has been already described. This process continuing for some time (2), a mulberry- like aggregation of cells is formed (3), which constitutes the material for the con- struction of the neAV indivi- dual. This process Avas for- merly very generally sup- posed to be preceded by the disappearance of the nucleus of the ovum or so-called ger- minal vesicle; but from re- cent observation it would appear that this does not take place, but that by its divi- sion it is bound up with seg- mentation of the cell in the usual manner of endogenous groAvth. But when impregnation does not take place, the ovum is destroyed Avithin the gene- rative organs by a process of liquifaction or solution. This is what occurs in by far the greater number of cases with the egg of the human female. And if we take into consideration the number of menstruations which occur during the whole time that a woman is capable of bearing, we shall gain some idea of the number of follicles requisite to supply the ova. This is, nevertheless, exceeded by far by the enormous production of f"nP 1 A.!" i* f* T* We have now to consider the destiny of the ruptured and emptied Graafian vesicle (fig. 538). The latter, soon after the fulfilment of its functions, is to be found filled up with cicatricial connective-tissue, con- stituting what is known under the name of the corpus luteum, after which it gradually disappears entirely in the stroma of the organ. Fig. 537.—Division of the mammal ovum (half diagram- matic). 1. The yolk divided into two globules (cells) with nuclei. 2. Quadrupled. 3. A large number of nucleated cells. 4. a, b, isolated cells. 546 MANUAL OF HISTOLOGY. If we examine a recently ruptured follicle very minutely, we notice in many instances the internal tunic projecting into the cavity on either side in folds (fig. 538, <**). These folds consist of young exuberant cell- j growths, and contain in their axes fasciculi of hard ill-de- veloped fibrous tissue. On the coming in contact of the ■ a apices of the folds a peculiar system of septa is formed of , the latter, the cells constituting the yellow substance of the corpus luteum. If, again, a completed corpus luteum (of a coav, for instance, His) be closely examined, it is found to have a peculiar radi- ating structure, produced by filamentous bands passing out from a central fibrous nucleus, the so-formed interspaces being occupied by a soft yellow substance. The whole is enclosed within the external membrane of the follicle to which the septa are attached. The vascularity of the corpus luteum is extremely great, and it contains, like the rest of the ovary, numerous lymphatic vessels. In fact, this yellow mass may be numbered among the most vascular parts of the Avhole body, so highly developed is its capil- lary network. Beside this vascular framework we find tAvo forms of cells in the yellow substance. In the first place, there are fusiform elements, 0*0338-0*0451 in length and 0*0056-0*0068 mm. in breadth, with oval elongated nuclei; and then, again, we meet with larger cells, 0*0226-0*0451 mm. in diameter, of various shapes, and containing yellow fatty granules Avithin them (fig. 95, a, p. 95). The former invest at all points the highly deve- loped vascular network of the part like the cells of a rudimentary adventitia. The latter, on the other hand, occupy the narrow meshes between these. Thus the general structure of the mature corpus luteum corresponds with that of the membrana interna of a fully developed Graafian vesicle. The yellow body, however, does not long remain in this condition of exuberant groAvth. It soon begins to undergo a process of retrograde development, diminishing at the same time in magnitude (fig. 538, e). This change commences in all probability in a decay of the afferent arterial tubes, which are now found to possess enormously thickened Avails (His). For some time we may still recognise, besides the vanishing yellow mass, the remains of the fibrous septal system, and external follicle membrane, distinguished by its dark broAvn pigments contained in cells. This colouring matter is laid down along the course of the vessels, and is possibly metamorphosed haemoglobin. As soon as this pigment has been absorbed, the yellow substance, formerly so abundant, melts gradually away with the adjacent ovarian tissue, until it is no longer recognisable. The time consumed in this retrogressive process varies considerably. When pregnancy does not supervene upon menstruation, the changes mentioned follow one another in rapid succession. But if gravidity takes ORGANS OF THE BODY. 547 place, the process is carried on with greater tardiness: the yelloAV body increases in magnitude, remains for some months at a high degree of development, and only recedes after four or five months. At the end of pregnancy it has not yet disappeared. These differences appear to be occasioned by the continuous increase of vascularity in the organs of generation in the latter case, compared Avith the more transitory excite- ment in the first instance. The corpora lutea have been classified, owing to this, into true and false. §279. We noAv turn to the consideration of the Fallopian tubes and uterus. The first of these may be divided into tAvo portions, namely, an upper and more or less tortuous half of greater diameter, knoAvn as the ampulla of Henle; and an inferior and much narrower half, Avhich leads into the uterus, the isthmus of Barkow. They present an external layer of con- nective-tissue belonging to the peritoneum, and beneath this a muscular tunic, consisting of longitudinal involuntary fibres, on the outside, and transverse fibres within. The cells of this coat, largely intermixed Avith con- nective-tissue, are extremely difficult to isolate. During pregnancy this is somewhat easier. The mucous membrane of the tubes is entirely destitute of glands. In the isthmus it is covered Avith small longitudinal folds ; in the ampulla Avith a series of very considerable ones, which are supplied, as I find in the pig, with a very complex network of looped vessels, and almost close the lumen completely. Its ciliated epithelium (p. 150), Avhich extends as far as the external surface of the fimbriae, moves in a ciliary wave directed towards the uterus. As in the mucous membrane of the uterus, so also here do we miss those goblet cells described by Schulze. The uterus or womb, although it undergoes numerous changes during the earlier periods of existence, owing to the processes of menstruation and pregnancy, is nevertheless in many points similar in structure to the tubai Fallopii. Its muscular tissue is, hoAvever, of greater strength, and its mucous membrane contains glands. The fleshy mass of the uterus consists of transverse, oblique, and longi- tudinal bundles of smooth muscular fibres, interlacing in every conceiv- able direction (p. 283). To a certain extent we may distinguish three layers, of which the middle is the thickest. Around the neck of the Avomb the fibres are arranged in transverse bundles, so as to form a regu- lar sphincter uteri. In this neighbourhood the contractile fibre-cells are particularly difficult to isolate if the organ is not in the gravid con- dition. In the mucous membrane of the uterus (Avhich is closely adherent to the muscular tissue, and exchanges with it many of its elements of form), we find both in the body and cervix a network of stellate and fusiform cells similar to those of the framework of lymphoid organs (Henle, Bind- OVBTl) Those bands of smooth muscular fibres which extend into it appear to terminate in its deeper strata. The mucous tissue of the vaginal portion was found by Lindgren to be traversed by vertical bands of elastic fibres connected with one another in arches near the surface. The body and parts of the neck also of the uterus present ciliated epithelial elements, described at a very early period as simple columnar cells without cilia. 548 MANUAL OF HISTOLOGY. But the lower portions of the cervix are lined by the same flattened epithelium met with in the vagina (p. 141). The surface of the mucous membrane varies also according to locality. In the fundus and body it is smooth and destitute of papillae, while numerous transverse folds of plicae palmate occur in the cervix, and many mucous papilke in its lower portion, with vascular loops m their interior. These are particularly abundant about the os, and are met with through- out fhe vagina. The same diversity is manifest in the occurrence of the glands. In the fundus and. body of the organ they are crowded together, subject to variations, in this respect, in different individuals. These glandulai utri- culares are found in the form of either branching or undivided tubes, about 1*13 mm. in length, and 0*0451-0*0751 mm. in breadth. They may, however, exceed in both directions. They are lined internally by columnar cells, and resemble in many respects the mucous glands of the sto- mach (§ 252), or crypts of Lieberkuhn of the intestine, though frequently convoluted at their inferior extremities. They are either entirely desti- tute of a membrana propria, or the latter is only present towards the mouth of the gland. In the pig the uterine glands are clothed within by ciliated epithelium, as Avas pointed out many years ago by Leydig. More recently the same species of epithelium has been found by Lott in these glands, in various other mammals. In the cervix they are no longer to be found (Henle), but are replaced by numerous depres- sions in the mucous tissue, lined Avith columnar cells, which appear be- tween its folds. These have been by some included among the glands of the organ. Both these structures, but especially the latter, preside over the secre- tion of the alkaline mucus of the uterus. JSot unfrequently the little pits just mentioned become occluded, and in consequence distended with mucus, They then present themselves in the form of small round vesicles, known as the ovula Nabothi. The large arterial tubes of the uterus, Avhich is very vascular, are chiefly situated in the external and middle muscular coats. The capil- lary netAvorks are to be found in the mucous membrane, the coarser in the deeper portions of the latter, the more delicate near the surface : they are rather irregular as to their arrangement, hoAvever. Both kinds of vessels are possessed, in the mucosa of the body of the uterus, of very delicate walls, Avhile in that of the cervix the latter are extremely thick (Henle). The radicles of the veins are wide, and the Avails of the latter are intimately connected with the tissue of the organ. They occur in the form of a dense plexus, especially in the middle layer of the muscle sub- stance, and are entirely Avithout valves. The arrangement here, as in the ovary, was pointed out by Rouget to be similar to that of the corpora cavernosa. Lympliatics were long ago observed in the gravid uterus, princi- pally in the outer portions of its walls, but those of the mucosa re- mained for a long while unknown. Here they were found, however by Lindgren, arranged (in the cervix) in retiform and arched passages, ending under the surface of the mucous membrane, either blind or in loops, and passing from thence into a deeper wide-meshed network of larger canals. The portio vaginalis possesses just the same kind of vessels. The mucous membrane of the body of the organ requires further observation. ORGANS OF THE BODY. 549 The nerves of the uterus have been very carefully investigated by Fran- kenhauser They are derived from the genital or spermatic ganglia, and through these from the so-called plexus uterinus magnus and p. hypo- gastric^ to which branches of the sacral nerves are given off On the posterior wall of the neck of the uterus is situated a ganglionic mass of considerable size, the ganglion cervicale of Lee. From this most of the nerves supplying the organ take their rise beside vaginal and vesical twigs. Only a very small number come from the p. hypogastricus. I he course of the nerves m the walls of the organ usually corresponds Avith that of the blood-vessels; it is, however, very hard to folloAV In regard to the ganglia found here, we refer to § 189. The termination also of the filaments in the muscular substance has been likeAvise dealt with in § 183. In the ligamenta lata bundles of unstriped fibres are to be found between their tAvo layers. The round ligaments are, however, still more richly supplied with these elements, besides Avhich they contain volun- tary fibres. On the other hand, the lig. ovarii are but slightly muscular. During menstruation the uterus becomes looser in texture and increased in volume owing to a great influx of blood into it at this time. At the same time, the glands of the mucosa increase considerably both in length and breadth. A discharge of blood takes place also from the gorged capillaries of the mucous membrane, the Avails of the latter being either ruptured in the act, or, by the passage, as some believe, of red cor- puscles through the uninjured Avails. The blood of menstruation, which is poured out at the external genitals (p. 121), is found besides to contain a large admixture of cast-off uterine epithelium. During preg?iancy the uterus undergoes a considerable increase in volume, affecting principally the muscular layers, and, as microscopical analysis has shoAvn, consisting in a remarkable groAvth of the contractile fibre-cells (§ 173) (which may noAv be easily separated from one another) as Avell as in a multiplication or neoplasis of the same, at least at the commencement ofthe period. Both the blood-vessels and lymphatics, as might be expected, partici- pate also in this increase in size. It is also an interesting fact, that the nerves of the uterus becomes thicker and grayer at the same time through thickening of their peri- neurium, while the individual fibrillae present a darker outline than before, so that they can uoav be folloAved farther into the parenchyma (Kilian). That the number of primitive fibrillae actually becomes larger is a matter greatly to he doubted. We must now bestow a feAV words on the most important of all the changes Avhich take place here, namely, the metamorphosis of the mucous membrane. Already before the arrival of the ovum in the cavity of the uterus this structure becomes thicker, softer, and more vascular. Further, its fibrous elements gaining in number, and the uterine glands increasing to four or five times their original length, a separation takes place between it and the inner surface of the uterus. Covering the ovum, noAv it is known as the decidua. After parturition a new mucous membrane and new glands are formed on the surface of the uterine cavity, a regeneration of Avhich neither of the tAvo tissues are capable under normal circumstances. The involuntary fibres of the womb undergo, about the same time, fatty degeneration, retrograde development, and partial destruction. 550 MANUAL OF HISTOLOGY. § 280. The vagina, an elastic tube, is to a certain extent a continuation, as far as structure goes, of the generative organs situated higher up. In it we find a layer of muscular fibres internal to a thick envelope of connective- tissue, loose without and dense within, and containing numerous elastic elements. This muscular coat consists of a layer of longitudinal fibres internally, and another of circular fasciculi externally. The mucous membrane of the part presents ridges and protuberances which go by the name of columnae rugarum, besides Avhich it is possessed of numerous papillae, similar to those of the cervix uteri, lying underneath its flattened epithelium. It appears to be quite destitute of mucous glands, and its secre- tions have an acid reaction. The hymen is nothing but a duplicature of mucous membrane rich in nerves and vessels. The vascular system of the vaginal Avail has a different arrangement for each of the three layers of the latter, and is remarkable for the high degree of development of the venous networks. But little is known, on the other hand, of the lymphatics of the part, but scattered lymphoid follicles have been met with in the vaginal mucous membrane of both man and the mammalia, and considerable patches have been observed to present an infiltration with lymph-cells. The nerves by which it is sup- plied are derived from the sympathetic and plexus pudendus. In man their termination in papillae has not been recognised, although their fibres are seen to divide; but in the rabbit the vaginal tunics are supplied with terminal bulbs and Pacinian bodies (Krause). See p. 333. The external female genitals consist of the clitoris and labia majora and minora. The clitoris is possessed of a prepuce or fold of mucous membrane continuous with that covering the glans, in which situation it is supplied with numerous papillae. Its corpora ca\Ternosa and bulbi vestibuli are analogous to the cavernous portions of the male organ (see below). The labia minora, or nympho3, are also small duplicatures of mucous membrane. They present numerous papillae and very vascular connective- tissue Avithout any fat cells. In them, as in the external parts of genera- tion, numerous sebaceous glands, without hairs, are to be found. The labia majora—folds of skin padded with fat—present on their internal surface all the characters of a mucous membrane, while externally their structure is that of the skin. On their outer surface they are covered with hairs, into whose follicles numbers cf sebaceous glands pour out their secretions. The vestibulum and opening of the vagina contains many ordinary racemose mucous glands, of which the largest, attaining a diameter of 15 mm. are known as the glands of Bartholin oxDuverney, which open with tolerably long excretory ducts into the vestibule. They correspond to Cowper's glands in the male generative apparatus. They are lined with Ioav columnar epithelial cells, and filled with a transparent mucoid secre- tion of viscid consistence. The blood-vessels of the part, Avith the exception of those of the corpora cavernosa have nothing remarkable about them. The lymphatics require closer study, as also the nerves which spring from the plexus pudendus of the sympathetic. The latter are stated by Koelliker to terminate in certain papillae of the clitoris in a manner similar to their arrangement in ORGANS OF THE BODY. 551 the tactile corpuscles. These observations have been since confirmed by the discovery of the presence in this organ of end bulbs, as they are called, and other mulberry-shaped terminal structures allied to them the genital bodies (Wollustkbrperchen of Krause, Finger) Pacinian'cox puscles have also been found in the labia majora, where they mer^e into the nymphae, and in the praeputium clitoridis (Schweigger-Seidel) " §281. The mammary glands, which only attain their full development in the female body and corresponding secretory power, belong to the great croup of racemose organs, as has been already re- marked (p. 358). They are peculiar, however, in that each organ does not empty itself event- ually into one single ex- cretory duct. In either breast the milk is poured out by from eighteen to twenty canals or galac- topherous ducts as they are called, each of which belongs to one of the primary lobes, or, better expressed, glands. Hav- ing already frequently referred to the nature of racemose glands, we need only remark here, that in this particular instance the end vesicles (formed of a homoge- neous membrana pro- pria) are more sharply defined one from the other, also that their form is spherical or pear- shaped, each having a diameter of betAveen 0*1128 and 01872 mm. (fig. 539, 1, 2, a). Their membrana propria presents, as in other allied glandular organs, a network of flattened stellate ceUs (Langer). Both the Icbules and lobes are enveloped in fatty connective-tissue, which gives to the breast its usual smooth rounded appearance. The former are also invested in the characteristic vascular networks of racemose glands. Of the lymphatics of the organ but little is known at present, and the nerves of the interior have but rarely been the objects of research. The influence of the latter on the process of secretion has likewise never been demonstrated experimentally. The interior of the Apsides is lined finally 86 Fig. 539.—The mammary gland; for the most part after Langer. 1. A lobule, from the interior of the gland of a pregnant woman. 2. a, vesicle; b, gland-cells. 3. Ducts from an infant. 4. Galac- tophorous duct from a boy 9 years old. 5. The same from a girl of 15. 6. The same from a grown man. 552 MANUAL OF HISTOLOGY. Fig. 540.—Gland vesicles from suckling woman, showing cells and capillary by ordinary cubical or polygonal cells about 0*0113 mm. in diameter (fig. °4lt'is an interesting fact, that here also that well-known network of very delicate tubules already mentioned (§ 195) may be rendered visible by in- jection, between the cells in the interior ot the acini (Gianuzzi and Falaschi). Accord- ing to Langer, however, no fibrous network can be discovered within the gland vesicles. The excretory ducts terminate amid the wrinkles of the mamilla with orifices about 0*7 mm. in diameter. Following them up into the* gland, we find them traversing the mamilla in the form of tubes measuring from 1*1 to 2*2 mm. across. At the base of the nipple they become dilated into what are known as the sacculi lactiferi, diverticula of from 4*5 to 6*8 mm. in trans- verse measurement. After this they then become narrowed again to 2*2-4*5, and con- tinue their course with rapid ramification doAvn to the ultimate vesicles. The excretory canals of the lactiferous system present a lining of columnar cells. Their walls are composed of connective-tissue and a layer of elastic fibres lying internally, and possibly also a few muscular elements occur here, as they are to be found around the lobules (Henle). Both the nipple and areola, hoAvever, remarkable for their dark colour and contractility, are possessed of these unstriped muscular fibres in abundance. In the former are to be found principally transverse bands intersecting each other, while longitudinal bundles are of less frequency. The arrangement of the bundles in the latter is chiefly circular, these being again crossed by radiating bands (Henle). The mamilla contains numerous papdlae, and the areola sebaceous glands. It may be well to turn now for a moment to the development of the organ. Like other glands connected with the skin (§ 200), the mamma takes its origin from the corneal germinal plate in the form of a growth inwards of the cells of the latter. In the fourth or fifth month of intra-uterine life it may be found as a solid mass of flattened globular or knobbed figure, enveloped in the fibrous layer of the skin, and consisting of cells of the rete Malpighi (Koelliker, Langer). A few weeks later (fig. 541) Ave remark that the knobbed process (a) has given off new solid buds (b, c) through cell proliferation. These are the first rudiments of the ducts of the primary lobes, and are distined to further gemmation (c). Up to the time of birth (fig. 539, 3), however, the rudimentary vesicles have not been formed. During all this time the border is always more highly developed than the central portions, as Ave might infer from the diskoid figure of the gland, and this continues to be its condition until the end (Langer). The ducts of the mammary gland of the infant present fibrous walls lined with small cells. At their ends we find solid aggregations of cells of irregular shape, the formative material for farther ramification. Even during childhood, and in girls (fig. 539, 4) as well as boys (5), the development of terminal vesicles has not yet begun ; the canals con- ORGANS OF THE BODY. 553 tinue to present the same structure as before. The female breast is, how- ever, at this period in a more perfect state than the male. At the commencement of puberty the formation of a considerable number of gland-vesicles takes place iu the female breast, and with tolerable rapidity, causing the organ to assume its well-knoAvn shape. But even still, and throughout the whole term of virginity, the gland does not attain Fig 541.—The mammary gland from a Fig. 542.—Degenerated mammary gland mature foetus, after Langer. a, central from woman 90 years of age. knobbed mass with smaller internal b and c, larger external buds. anything like its full development, for which the supervention of the first pregnancy is requisite. In this state of maturity it remains through- out the whole period of fecundity, decreasing, however in size when at rest, and losing some of its vesicles. Finally, Avith the decline of the reproductive powers a retrograde development of the mammary gland takes place, Avith gradual disappearance of all its terminal vesicles, and destruction of the smaller ducts, until eventually nothing but fatty tissue is to be found in its place. It is represented in this condition in fig. 542. Here the canals only are to be found; everything else has dis- appeared. The interstitial connective-tissue appears rich in elastic fibres (Langer). The mammary gland of the male (fig. 539, 6), with very rare exceptions, never attains the same degree of. development as in the female. In it we generally find nothing but a system of ducts, varying greatly in size, no trace of terminal secreting vesicles being apparent (Langer). § 282. Milk is an opaque bluish or yellowish-Avhite fluid, without odour, sweetish to the taste, with a slightly alkaline reaction, and a sp. gr. usually of about 1 -028-1 *034. When kept in a state of rest it separates into two strata—an upper, thick, fatty, and white (cream); and a lower of much thinner consistence. Some considerable time after this a process is set up, in Avhich its alkaline reaction is changed for an acid by the conversion of su^ar of milk into lactic acid. As a consequence of this, the casein con- tained in the fluid coagulates, a change which is also effected by contact ivith the mucous membrane of the stomach (p. 17). Anatomically, milk consists of a transparent fluid, in which innumer- able fatty globules are suspended : it is therefore an emulsion. 554 MANUAL OF HISTOLOGY. These alobules (fig. 5 43, a), present the usual optical characters of oil drops, and anAverage^dameter of 0^0023-0*0090 mm. Under ordinary circum- JSnces they 1o not coalesce, but do so readily on the addition oT ^etic -d showing that each particle possesses a very delicate membrane of some protein substance, probably casein. The microscopic appearance, however, of milk, which is secreted in the last days of pregnancy,_ and immediately after parturition, continuing sometimes, even under abnormal conditions, for a longer period, is quite different. This fluid is knoAvn as colostrum. It is of strong alkaline reaction, rich in solid con- stituents and salts, and contains, besides fatty globules, FUr' t5s4o3fhumanmnk" otner bodies to which the name of colostrum cor- !Tgiobuies;T ™»l0- puscles has been given. These (b) are spherical struc- strum corpuscles. tureg of from Q.Q151 to 0*0564 in diameter, consisting of an agglomeration of oil globules, held together by some species of cement. Sometimes a nucleus may be found in them, besides Avhich they are endoAved with the poAver of contractility, sluggish no doubt, but unmistakable (Strieker, Schwarz). Taking milk chemically, we find in it, besides water, casein (p. 17), neutral fats (p. 26), and a kind of sugar known as sugar of milk (p. 33); further, extractives and mineral constituents, free carbonic acid, and nitrogen, gases, and small quantities of oxygen (Hoppe). Even blood and bile pigments may also be abnormally present. Casein is generally supposed to occur partly in combination Avith soda, dissolved in the watery portion of the milk, and partly, as we have already remarked, coagulated in the form of delicate membranes around the milk- globules. The amount of phosphate of calcium present in this fluid is quite remarkable. Albumen also appears to exist in milk, but in colos- trum it is undoubtedly present. The neutral fats of the milk consist first of the ordinary fatty matters, and then of those which, on saponifi- cation, set free bidyric, capronic, caprylic, and capinic acids (p. 25). We have already spoken of them in detail in an earlier section. The sugar of milk is found in solution, as also the extractives and the majority of the mineral ingredients. The latter consist of chlorides of sodium and potasium, of combinations of phosphoric acid Avith the alkalies and earths, and of soda and potash Avith casein; iron is also present. The insoluble salts usually preponderate. The name " fairy's milk" (Hexenmilch) has been applied to a peculiar milky secretion produced by the mammary glands of infants for some days after birth. In the quantitive analysis of human milk we must bear in mind that it varies considerably according to age of the individual, and nature of food indulged in by the latter. These variations are much more decidedly marked in many of the mammalia. The following is an analysis of Simon's:—- parts contain— Water, ..... . 880*6 Casein, ..... 370 Sugar of mdk, .... 45*4 Fatty matters, .... 34-0 Extractives and salts, 30 ORGANS OF THE BODY. 555 The proportion of casein in woman's milk is, according to Simon, about 3*5 per cent, on an average ; that of fats, 2*5-4 per cent.; of sugar of mdk, between 4 and 6 per cent, ; of salts (among which phosphatic earths pre- dominate), 0*16-0*20 per cent. The average amount of milk secreted daily by the human female, during the period of lactation, is somewhat over 1000 grammes. About 50 or 60 grammes may be produced by one breast in two hours (Lam- perierre). The use of milk is, as is Avell knoAvn, for the aliment of the infant. It is secreted at the expense of the nutritive material of the mother's blood, and may be designated as the prototype of all aliment. If Ave compare the ingredients of milk with those of the plasma of the blood (p. 115), Ave find that the mineral constituents of the latter may have simply transuded into the former, somewhat in the same manner as that in which they find their way into the urine. But the three series of organic substances are not to be found as such in the blood, or, if so, only in small amount. To the first of these, casein and sugar of milk belong, the sources of which may be regarded as albumen and grape sugar; to the third the fatty matters. All this seems to indicate an inherent poAver in the mammary gland of causing a species of fermentation, as also of producing within its cells a part, at least, of the oily matters found in the milk. The mode in which the secretion of the mammary gland is produced in the interior of the \*esicles is simdar to that in which the sebaceous matter of the skin is formed. The gland-cells become enlarged by the generation within them of oil globules (fig. 539, 2, b), and are in this way physiologically destroyed, at least in many cases, although the membrane- less body of the contractile gland-cell no doubt frequently enough simply disgorges its fatty contents. During the less active formation of the colostrum these cells, or fragments of them, are carried off in the watery portion of the milk. The gland-cell of the suckling woman is regarded by us as a very transitory structure. § 283. The male generative apparatus consists of two testicles, enclosed in the scrotum, and invested Avith their several tunics; of the excretory ducts, emptying themselves into the urethra; of the copulative organ; and, finally, of accessory structures.- Among the latter we have the single prostatic gland, a pair of glands known as Cowper's, and the vesiculo' seminales. The testis, Avith its accessory epididymis, is a gland consisting of a multitude of fine and very tortuous tubules, known as the tubuli semi- niferi. The whole is covered by a fibrous investment, to which the name of tunica albuginea, s. propria testis (p. 227), has been given,—a tough, whitish membrane of considerable thickness. It is again contained within another sac, the tunica vaginalis propria, a serous investment, whose internal portion (t. adnata) cannot be distinguished from the albuginea. Finally, the testicle and spermatic cord are enveloped in the t. vaginalis communis, a strong bag, composed of a serous and fibrous portion, which contains, around its junction with the vaginalis propria and epididymis, a number of contractile fibre-cells (Koelliker). Upon this coat the striped fibres of the cremaster muscles are situated externally. This vaginalis communis is connected without with the muscular tunic of the scrotum, 550 MANUAL OF HISTOLOGY. the dartos (p. 283), by formless connective-tissue Finally, the whole is covered by a thin layer of true skin quite destitute of fat. If Ave seek to remove the albuginea, we observe that numerous but im- perfect fibrous septa are given off by the latter, and penetrate into the interior of the gland. . . , These partitions, which divide the parenchyma into lobules (fig. 544, b) Fig. 544.—The human testicle, after Arnold, a, testicle Fig- 545. — Seminiferous divided into lobuli 6; c, tubuli recti; d, rete vasculosum; tubes from a human tes- e, vaseula efferentia;/, coni vasculosi; g, epididymis; tide, o, membrane; b. h, vas deferens; i, vas aberrans of Haller; m, branches of cells. the internal spermatic artery, with their arrangement in the gland n; o, artery of the vas deferens, anastomos- ing at p with the last named vessel. of conical form, Avhose apices are directed inwards and upwards, con- verge in the superior part of the organ, to be inserted into a dense wedge- shaped mass known as the corpus Highmori, whose base is attached to the albuginea. Each of these lobules is made up of several extremely long semini- ferous tubules, about 0*1128-0*1421 mm. in diameter, folded on them- selves several times. These may be seen to divide frequently, and anas- tomose, and to terminate, not blind, but in the form of slings and loops. At the apices of the lobules the. seminiferous tubules, becoming rapidly narrowed, open into a straight passage, which goes by the name of the tubulus rectus (c), and which penetrates the corpus Highmori (lined with Ioav columnar cells), and forms what is called the rete testis (d), by inter- communication with the vessels of the same kind. From this network the larger tubes, or vaseula efferentia (e), take their rise. Their number is from 9 to 17, and their course at first straight until they pierce the albuginea, after Avhich they become again very tortuous, and are arranged in a series of conical lobes, known as the coni vasculosi (f), which form the caput epididymis. ORGANS OF THE BODY. 557 Fig. 546.—From the testis of a calf. 1. Transverse section of a seminiferous tubule. a,b. walls of the latter; c, capillary network; d, connective-tissue framework; e, lymphatic canals. 2. Side view of the wall of a seminiferous tube; a and b, wall o^a? n SraduaIly comkine to form one single Avide canal (g g) 0*376 /-0*45 mm. in diameter; which turns and twists upon itself'still further in forming an elongated body known as the corpus and cauda epididymis. By degrees this tube, of which the epididymis is composed, becomes less tortuous and of greater calibre, its diameter amounting on an average to 2 mm. It is now known as the vas deferens (h). Frequently before this it receives the addition of a short ccecal branch, the vas aberrans of Halter (i). Turning iioav to the structure of the seminal gland, we find in the first place that it presents a sustentacular substance. This is found in the form of fibres cf connective- tissue (fig. 546, 1, d), radiat- ing from both septa and capsule throughout the whole organ. In this connective-tissue numerous cells and nuclei are encountered in young animals : its bands vary in thickness; in the calf from 0*0564 to 0*0113 mm. These bundles of connective- tissue (Mihalcowicz) are enve- loped in those flat membraneous cells of which we have already spoken (§§ 130, 223), and to which Ave shall again have occasion to refer in considering the arachnoid. These cells cover like a membrane both seminal tubules and blood-vessels, leaving, however, chinks between them, Avhich serve a purpose in the lymphatic circulation. In the human and mammalian testicle besides a number of pecuhar cellu- lar elements, undergoing pig- mentary and fatty metamor- phosis, the " interstitial cells," are met with, at times in great abundance. They are usuady arranged in bands, their diameter be- ing in the cat 0*014-0*020 mm. They may envelope the vessels like a sheath. The interstices of this sus- tentacular substance are occupied by the seminiferous tubules (figs. 545, 546, 1 a; 547, a, b) whose diameter * ' ' „ d, lymphatics, is on an average Irom .1.1.1, 0*1128 to 0*1421 mm. By the aid ofthe microscope we learn that tlie mem- brana propria is represented by a coat (sharply defined from the interstitial connective-tissued of tough texture, and fibrous or banded structure, contain- ing elongated nuclei (fig. 545, a; 546, 1 a, b, 2 a, b). Its thickness ranges from 0*0046 to 0*048 mm. In man this wall is particularly well marked. It consists, according to Mihalcowicz, of several layers of flattened cells united with one another in the form of a membrane. The most interna] Fig 547. —From the testis of the calf. a. seminiferous tubules in profile; b, in transverse section; c, blood-vessels; layer is quite impervious ; but the external is open and net-like. 558 MANUAL OF HISTOLOGY. The interior of these tubes is filled Avith cells, of which the most peri- pheral may cover the membrana propria in a manner similar to epithe- lium. They are usually roundish or polygonal, and from 0*0113-0*0142 mm. in transverse section. They are composed in young subjects of a finely granular, rather pale substance (containing yelloAV pigment in man), which becomes charged in the course of years Avith an ever-increasing number of fatty granules. These cells of the testes have been observed even in embryos to be endoAved Avith contractility, and to possess the poiver of amoeboid change of form (La Valette St George). Recently, hoAvever, a more complex structure has been ascribed to the seminal tubes. In man and the ox, for instance, a framework of flat stellate cells with membraneous processes is stated to exist in their interior (Sertoli, Merkel, Boll). We regarded these, the " sustentacular cells " of Merkel, as the same network to Avhich we have already had such frequent occasion to allude in dealing with the racemose glands. Mihalkowicz, on the other hand, in his excellent Avork, declares this appearance of sustentacular cells to be an artificial production caused by the coagulation of an albumi- nous material between the seminal cells. Such is the structure of the seminiferous tubes as far as the rete testis, in Avhich for the time being their external fibrous tunic is fused into the connective-tissue of the corpus Highmori. The tubes, Avhich leave the latter as they increase in size, obtain an additional layer of smooth muscular fibres, Avhich is further strengthened lower doAvn in the body of the epidi- dymis by two coats of longitudinal fibres, an external and an internal. This arrangement Ave shall again meet Avith in the vas deferens. We have already (p. 150) alluded to the peculiar ciliated epithelium of the epididymis. The blood-vessels of the testes are branches of the internal spermatic artery. They penetrate into the interior of the organ-form Avithout, and from the corpus Highmori, and take their further course along the septa dividing as they go. Finally, they break up into a long-meshed, rather loose capillary netAvork of somewhat contorted vessels, from 0*0128 to 00056 mm. in diameter (fig. 546, 1, c; 547, c), which invests the semini- ferous tubes. The vascularity of the epididymis, which is supplied by the arteria vasis deferentis Cooperi, is no less considerable. The veins present the same arrangement as the arteries. The lymphatics of the parenchyma of the organ, lined by the special cells of- such vessels (Tommasi), occupy the soft interstitial connective- tissue of the former, arranged in a close network of canals (fig. 516 1, c; 547, d). In transverse sections of the seminiferous tubes, it may be seen that these lymphatic canals form regular rings around the latter, of pas- sages from 0*0128 to 0*0292 mm. in diameter, and strongly dilated at the points of junction Avith each jather. Steady injection at last drives the fluid employed through the external cellular layers of the Avails of the seminiferous tubes. The most internal layer alone is entirely impervious (Mihalkowicz). The blood-vessels, also, are here and there ensheathed in lymph streams. From the rings just mentioned other lymphatic canals are b) commences with a constricted tozoa. a, view of the neclc, succeeded by a somewhat thickened por- broad surface; b, in pro- tion, gradually becoming thinner and finer, until at last it attains such a pitch of tenuity as to baffle microscopic analysis. It may be followed to a length of about 0*0451 mm hov a long time it was supposed that the spermatozoa only consisted of these two parts, and that they were quite homogeneous throughout without any distinction between envelope and contents. More recent observations, with the aid of the stronger systems of lenses of the present day avouId seem to place this view in question. The reports, however, of Valentin, Grohe and Schweigger-Seidel on the subject do not ve entirely agree. J From the able researches of the last-named observer it would appear that the tail of the spermatozoon (fig. 549) may be divided into two por- tions, often sharply defined one from the other, and different in diameter and in chemical and optical characters: these are, first, the middle portion (6), as it is called; and, secondly, the delicate terminal filament (c). In those instances in which the head of the human spermatozoon possesses the length mentioned above, of 0-0045 mm., the middl^S ORGANS OF THE BODY. 561 is 0*0061, and the terminal filament 00406. Both the head and middle portion appear rigid, leaving the end fibre alone movable. That a differ- ence exists between envelope and contents in the sper- matozoa, as maintained by Grohe and Schweigger-Seidel, Ave do not think has been yet clearly proved. Throughout the whole animal kingdom semen is pos- sessed of certain definite form-elements. But though the prevailing shape of these spermatozoa is filiform in all animals, nevertheless they present extremely interesting and considerable varieties of appearance, reminding us of the similar though much less markedly characteristic peculiarities of the red blood-cells (§ 68). The narrow limits of our Avork, unfortunately, do not permit us to enter deeper into this very interesting subject; but we cannot relinquish it without pointing to the probable safe- guard against hybrid impregnation which exists in these Fi^- 549-—sPer- strongly-marked peculiarities,—a kind of aid to the per- sheS°a l^ter sistence of distinct species. Besides this, in many animals dd^TVelt- this motion has been missed, while in others a lazy amse- *. middle por- boid change of form only could be observed. tlon; c'taiJ* From a chemical point of view the spermatozoa of the mammalia con- sist of a resistent metamorphosed albuminous substance, rich in lime, Avhich approaches in quality to elastin. They withstand for a very long time the process of putrefaction, and even oppose a determined resistance to the action of the mineral acids, dissolving, on the other hand, but still very slowly, in caustic alkalies (Koelliker). Owing to the large propor- tion of mineral ingredients in the spermatozoa, they preserve their form, although subjected to a red heat. The composition of pure semen,—that is, the secretion of the testicle,— was studied many years ago by Frerichs, especially that of the carp, but also of the cock and rabbit. In his observations he found the fluid neutral, resembling a dilute solution of mucus, and containing a certain amount of albumen. Chlorides of the alkalies, and small quantities of phosphates and sulphates of the same, were present in its residual ash, as also phosphate of magnesium. The dry substance of the spermatozoa contained 4*05 per cent, of a yellow matter like butter, probably containing phosphorus, and, we may now add (?), probably also cerebrin and lecithin. Besides this, 5*21 per cent, of ash constituents, among Avhich lime and phosphoric acid pre- sented themselves. Pure semen from the horse has 1806 of solid ingredients; that of the bull 17*94, of which the metamorphosed protein substance of the sper- matic filaments amounts to 13*138 per cent, lecithin (?) to 2*165, and mineral matters to 2*637 per cent. (Koelliker). Semen, as discharged from the urethra, is richer in water, from the addi- tion of the secretions of the accessory glands : that of man was found by Vauquelin to contain, on the Avhole, only 10 per cent, of solid matters. The substance which causes semen to coagulate after emission, named long ago by Vauquelin "spermatin," appears to be an albuminate of sodium (Lehmann). The development of the spermatozoa Avas formerly supposed to take place from peculiar cells in the seminiferous tubules. But the process was first accurately described by Koelliker. At the time when semen first begins 562 MANUAL OF HISTOLOGY. to be formed (puberty in man, rutting season in animals), most of the glandular epithelium cells of the seminal tubules undergo division, by which act a multitude of delicate, pale, and transparent elements of spherical form are produced, with vesicular nuclei of 0*0056-0*0079 mm. in diameter, sometimes single, sometimes ranging from 10 to 20. These cells vary in diameter between 0*0113 and 0*0074. From them the seminal filaments are supposed to be developed, and, moreover, from the nuclei. At first it Avas thought that, in the interior of each of these vesicular nuclei, a seminal element took its rise; but Koelliker asserted later that the whole nucleus becomes converted into a spermatozoon. This he stated to take place by its becoming elongated and flattened, and dividing into an interior dark and posterior lighter portion, and sending out at one end a filament destined to increase more and more in length, while the nucleus itself assumed gradually the char- acteristic form of the head. The spermatozoa so formed Avere supposed to lie eventually within the cells, in number corresponding to the original number of nuclei. Their arrangement there Avas stated to be regular when more than a few were present, namely, Avith their heads close to one another and the tails like- wise parallel, bent according to the amount of space left to contain them. A smad number of these formative cells Avere supposed to rupture before leaving the testis, setting free the spermatozoa; but by far the largest proportion of the latter to be liberated in the epididymis. But these theories, the correctness of which was for some time believed to be beyond doubt, have been since found to be untenable, and the genesis of the spermatozoa is at the present day a point of great obscurity. Henle was the first to point out, some years ago, another order of things from that just mentioned. He found, namely, tAvo kinds of cells in the seminiferous tubuli,—one Avith coarsely and another Avith finely granular, sharply-defined, nuclei. He supposed the head to take its origin from the latter, which project beyond the surface of the cells; further, that the filamentous process does not spring from the interior of the cell. In the last vieAv he is supported by Schweigger-Seidel. This observer regards the spermatozoon as a single ciliated element formed by the metamorphosis of a whole cell. The nuc- leus, he believes, is transformed into the head, and the middle portion to be derived from the remainder of the cell-body, while the terminal filament represents a cilium. According to Henle, cells with rolled-up filaments never occur as normal structures in the seminiferous tubes, Avhich is also denied by both Schweigger-Seidel and La Valett-St George, Avith Avhom we also entirely agree. From our OAvn, but, we must confess it, rather hasty, observations (fig. 55a), the process of the formation of spermatozoa appears to be as follows :—The nucleus of the primary seminal cell (a) advances to the peri- phery (b). Then the formation of the caudal appen- dage commences (c). The nucleus then passes beyond the original boundary of the formative cell, clothed in a thin layer of protoplasm (d). Later still, the nucleus, with this cover- ing of protoplasm, forms the head of the seminal element while the appendage of the cell-body grows out into a long thread (e) Finally (/) Fig. 550.—Mode of forma- tion of spermatozoa in the mammal. 1, head; 2, middle portion; 3, terminal filament. ORGANS OF THE BODY. 563 we have the head or nucleus (1), the middle portion or remainder of the cell-body (2), and the filament, the elongated cilium (3). § 285. The most striking and important peculiarity of the seminal elements, and one recognised as such ever since their discovery, consists in their movements. These, Avhich were in olden times accepted as a proof of their independent individual life (ivhence the name "spermatozoa") appear to be very nearly allied to the phenomena of ciliary motion (§ 99), and, like the latter, baffle at present all explanation. If semen be taken from the seminal tubes of some freshly slaughtered mammal, it will be found, as a rule, that the movements in question have not yet commenced. But if a drop of the fluid, immediately after emission from the urethra, be placed upon a glass slide under the microscope, innumerable spermatozoa are observed moving in all directions in the utmost confusion. Closer inspection shows us that the individual elements of the semen execute a series of movements, consisting in alternate flexion and exten- sion, and undulating motions like those of the lash of a whip, by means of which the whole structure is propelled from place to place. Though tempted for a moment to compare this Avith the independent hurrying to and fro of a host of infusoria, Ave very soon observe the most marked points of distinction. We miss^ in the first place, the spontaneity of the latter organisms,—that swimming in definite directions and avoidance of obstacles which characterise their movements; also that momentary acceleration and slackening in pace. The rate of progression moreover of the spermatozoa is by no means very great, several minutes being consumed in advancing even the distance of an inch. Like the motions of the cilia, those of the seminal filaments commence, after a time, to decrease in rapidity and the structure dies. We remark the intensity of the whip-like undu- lations of the fibre growing less and less, until at last the movements of ' the latter cease to propel the spermatozoon any farther, and all evidences of life become extinct. Let us noAv consider the conditions of these movements. Their dura- tion, in the interior of the male organs of generation or in emitted semen, varies in these different classes of animals. In birds they cease most rapidly, often Avithin a quarter of an hour. Among the mammalia they persist for a much longer period, at times almost for a Avhole day. Thus in human semen, after pollution, the spermatozoa may be observed still to retain the poAver of motion sixteen or tAventy hours after emission. Among the Amphibia they last much longer, and in fish longer than in any other animals. Here they may be seen under favourable conditions four days after the discharge of the semen (Wagner). We are thus reminded again of ciliary motion. If the temperature be reduced to beloAv freezing-point, the movements of the spermatozoa cease; but even after remaining four days in a congealed state they may regain their power of locomotion on being Avarmed. Cooled down to - 17 O, they die; as also on being heated up to + 50 C. (Mantegazza). As to the effects of the addition of other fluids to the semen, we find that indifferent matters of a certain average concentration,—as, for instance, solutions of sugar, urea, glycerine, and neutral salts of the alkalies and earths —may be added without arresting the motion of the spermatozoa, while very dilute solutions cause their destruction. Very concentrated fluids also prevent by their viscidity any play or motion in the filaments. 564 MANUAL OF HISTOLOGY. The same mechanical obstacles to the motions of the spermatozoa are pre- sented by matters which become simply gelatinous in Avater; such as vegetable mucous. Those re-agents, also, which act chemically on either the seminal filaments or fluid,—as, for instance, mineral acids, metallic salts, acetic acid, tannic acids, ether, alcohol, and chloroform,—all bring the lively movements of the former to an end. They may be best exa- mined in serum, white of egg, and vitreous humour; as also in the contents of the vesiculae seminales, prostate, and Cowper's glands, as the natural ingredients of the semen. In the secretions of the internal female organs of generation their motions are for a long time preserved. Here they may be observed, in the mammalia, wandering hither and thither for days, under the favouring influence of the animal heat of the parts. The acid mucous of the vagina, as Avell as the transparent and viscid secretion of the cervix, are said to put an end to the movements of the spermatozoa. Urine, Avhen neutral or slightly alkaline, has no very great effect upon the latter; but when strongly acid or alkaline, its action is very well marked. In alkaline milk or mucus the phenomenon of motion is quite evident, while saliva has the same effect on it as water. This is peculiar, bringing all movement rapidly to an end ; but it is pre- ceded by increased activity for a short time, during which the sperma- tozoa hurry about Avith great rapidity, striking and lashing with their tails. Soon, however, they come to a state of complete rest, when the under end of the filament is usually observed to be folded round the upper portion, like the lash round the stock of a Avhip. It is an interest- ing fact that such motionless spermatozoa may be again called into activity by surrounding them with saturated solutions, such as those of sugar, white of egg, and common salt, and also, Avhen in too strong solu- tions, by subsequent addition of water,—an indication of the important part which endosmosis plays in the phenomenon. We have already seen in an earlier section that the caustic alkalies have a most stimulating action on the ciliary motions: the same has been observed by Koelliker to be the case with the elements of semen. Recent research has shown that the spermatozoa penetrate into the interior of the ovum in order to impregnate it, moreover,—in the mammalia in considerable number. This entrance appears here, as among all the vertebrates, to be effected by the efforts of the spermatozoa, and carried out by the movements of their thinner portion. A special opening (micropyle), to admit them, has not yet been demonstrated in the zona pellucida, but those radiating lines seen on the envelope of the ovum may possibly represent, as pore-canals (§52), such passages for the spermatozoa which may be enlarged by the latter. These, on penetrating into the yelk, become motionless, and soon after break doAvn and become fluid. § 286. Turning noAv to the thick-walled vasa deferentia, it will be remembered that they take their origin gradually from the passages of the epididymis, and are therefore possessed of a similar structure to the latter. They are made up of an external fibrous investment, then a muscular coat of considerable thickness, composed of three laminae (already mentioned in speaking of the epididymis), an external strong and internal Aveak layer of longitudinal fibres, together with a middle tunic of circular bundles which is the strongest of the three. The mucous membrane with Avhich they are lined is covered by columnar cells, 0*0501 mm. in height Near ORGANS OF THE BODY. 565 the lower end of the vas deferens is a fusiform dilatation, the " ampulla " of Henle, from which a number of blind diverticula, leaving the main tube, pass at very acute angles upwards into its walls. In this expanded portion of the canal the mucous membrane differs from elsewhere : it is thicker and rugose, and presents a number of pits and saccules. In the walls of the ampulla further vermiform glands pre- sent themselves, filled with polyhedral cells, and containing molecules of a yelloAV and brown pigment (Henle). The nerves of the vas deferens possess ganglion cells, and are medullated. Their mode of termination is not yet known. The thin-walled vesiculae seminales have also a simdar structure. They are, in fact, little else than highly-developed diverticula of the same stamp as the ampulla of the vas deferens, but branching. They are partly designed as receptacles for the semen as it is secreted, and partly as secreting organs themselves. Their walls are supplied Avith scattered bundles of smooth muscular fibres. Within them we find a transparent fluid which coagulates into a gelatinous substance on exposure to the air, becoming subsequently liquid again. This is manifestly the same matter as the semen dis- charged from the uretha (§ 284). According to Gerlach, the rugose mucous membrane with which they are lined contains numerous compound mucous glands, Avhich are stated by Henle to be of the tubular kind, and by Klein to be only pits. Their structure is othenvise similar to that of the ampulla. The ejaculatory ducts correspond also in structure Avith the last-named organs. Their calibre decreases greatly in their course through the prostate. In the more dilated portions their mucous membrane presents similar folds, tubular mucous glands, and yellow and brown pigment granules, as the ampulla and vesiculae seminales. Within the prostate the muscular layer of the ejaculatory duct gives place to cavernous tissue (Henle), and the mucous membrane becomes thinner, smoother, and loses its glands. The prostate, the largest of all the organs connected with the male generative organs, is an aggregation of glands belonging to the racemose type, but presents, besides, many peculiarities. With Henle we may con- sider it as divided into three portions, namely, the two sphincters of the bladder, the internal formed of unstriped fibres, and the external with an increasing number of striped elements ; and finally, the body of the gland just mentioned. Besides a fibrous tunic with an admixture of muscle elements, the prostate is enveloped in a tough yellowish membrane, con- sisting chiefly of smooth muscular fibres. This latter sends off into the interior of the glandular mass a number of processes forming a massive framework, and making up a considerable portion of the whole organ. The separate elements of the gland, in number varying from 15 to 20, appear to be of the racemose kind In them we find pear-shaped vesicles of 0*1254-0*23 mm. in diameter, lined Avith columnar epithelial cells. The ducts of the gland are fine, surrounded by a muscular coat, and lined with the same columnar epithelium : they empty themselves singly, in the neighbourhood of the colliculus seminalis, into the urethra. The vascularity of the organ is considerable, its vesicles being enve- loped in capillary networks. The lymphatics and mode of termination of the nerves of the prostate which present ganglion cells are still unknown. The secretion of the prostate is probably allied to that of the vesiculae seminales. In both we find an albuminous matter freely soluble in acetic acid. 566 MANUAL OF HISTOLOGY. Those concentrically laminated concretions known as prostatic calculi are composed of this substance. In old men almost every prostate con- tains some of these bodies, which are often seated in the excretory ducts. The sinus prostatica or, as E. Weber has named it, the uterus mascu- linus, is a slender saccule, from 7 to 14 mm. in length, lying in the sub- stance of the prostate. Like the coliculus seminalis it is lined with laminated epithelial plates, has a fibrous wall intermixed Avith muscle elements, and is enveloped in a thin layer of cavernous tissue. It opens at the summit of the colliculus seminalis between the two orifices of the ejaculatory ducts. Cowper's glands are small, round, and more or less lobulated bodies, a feAV lines broad. They possess a fibrous envelope, containing some isolated bundles of striped muscle, and present the usual structure of race- mose glands. In their lobules, which are separated from one another by connective-tissue mixed with contractile fibre-cells, we find small gland vesicles lined Avith columnar cells. The someAvhat wide ducts of the lobes are clothed with flattened cells. In the interior of the organ they unite to form a number of large passages, which give to a transverse section of the organ an appearance as though sacculated. Subsequently, hoAvever, they combine at acute angles to form one single trunk. §287. There still remain to be considered the urethra and copulative organ of the male. The first of these consists, as is Avell known, of three portions,—the pars prostatica, passing through the prostate gland; the p. membranacea, a middle portion, made up of an independent membrane ; and a third com- pound part, Avhich is the longest of the three, and named p. cavernosa. This latter belongs to the penis, in which it is enveloped in a spongy body, the corpus cavernosum, s. spongiosum urethrce, which forms with its anterior extremity the glans penis. Associated with this spongy mass are two other structures of a similar nature, the corpora cavernosa penis, Avhich, together with an external covering of skin and several voluntary muscles (m. m. ischiocavernosi and bulbo-cavernosi), make up the copulative organ of the male. The urethra of man presents for consideration, internally, a mucotfs membrane, covered in the prostatic and membranous portion with flattened or transition cells, but lower down with cylinder epithelium (§ 91). This mucosa is invested, again, in a fibrous tunic, rich in elastic elements and of looser texture, in whose interstices a cavernous tissue is formed (Henle). External to this, again, is a layer of involuntary muscular tissue formed of longitudinal fibres internally, and transverse externally. The three portions must, however, be considered separately. The first thing which strikes the observer in the prostatic portion is the prominence of the colliculus seminalis, to which Ave have already referred in speaking of the ejaculatory ducts and prostate. It is covered by a longitudinally Avrinkled mucous membrane, and consists of elastic tissue (intermixed with bundles of contractile fibre-cells), which bears all the characters of cavernous substance. This spongy tissue is near the surface displaced at certain points by glands similar to those of the pros- tate, situated partly in the mucosa and partly deeper (Henle). The mucous membrane of the pars prostatica is seen to be arranged in fine intersecting folds, chiefly, however, longitudinal: it contains glandules identical Avith those just mentioned. ORGANS OF THE BODY. 567 Iii the middle or membranous portion of the passage under the mucous membrane a long-meshed cavernous tissue again presents itself. The organic muscular layer, on the other hand, is weaker, and covered by bundles of the musculus urethralis, which consists principally of trans- versely arranged bundles of striped fibres. But the unstriped muscular tissue of the pars cavernosa is even less developed still. Here the mucous membrane is covered with cylinder cells, which give place to a coA'ering of flattened epithelium at a greater or less distance from the mouth of the urethra. The last-named portion of the urethra contains farther little depres- sions or pits, the lacunae Morganii, which are not glandular in their nature; also isolated small and ill-developed racemose glandules, known as glands of Littre, whose vesicles and ducts are lined with cylinder epithelium. These do not appear to exist in the pars membranacea (Henle). Just a feAV words in regard to the skin of the penis. This is thin and loose down to the free edge of the prepuce, and is possessed of fine downy hairs, which decrease in length beloAv, and into whose follicles sebaceous glands empty themselves. Its very elastic subcutaneous areolar tissue presents longitudinal bundles of involuntary muscle-fibres, prolongations of the tunica dartos of the scrotum, and is quite devoid of fat-cells. This subcutaneous tissue invests the whole organ down to the base of the glans : it is known as the fascia penis. At the root of the member it is condensed into an elastic band—the ligamentum suspensorium penis. The connective-tissue binding the two laminae of the foreskin together manifests the same distensibility, but is destitute of fat: it is intermixed with muscular elements. The surface of the glans is covered by a delicate membrane, closely adherent to the cavernous tissue beneath. This membrane is possessed of very numerous papdlae arranged in rows converging towards the orifice of the urethra, and obscured by the flattened epithelium covering of the part. On the corona glandis we may frequently observe larger papillae, measuring from 0*9 to 0*5 mm., and appearing as white specks through the membrane or bulging out the latter. The internal leaf of the foreskin, smooth and without wrinkles, presents all the characters of a mucous membrane. It is quite destitute of hair and convoluted glands, but is supplied with numerous tufted papillae. On the inner surface of the prepuce are situated a number of sebaceous follicles, knoAvn as Tyson's or Littre's glands. These occur in varying number and form, and are found at times also upon the surface of the glans, especially in the vicinity of the fraenum. Their secretion mixes with the epidermal scales of the part when shed, and so assists, though, in a very minor degree, in producing that tallowy substance, known as the smegma preputii, Avhich collects sometimes underneath the foreskin. Each of the corpora cavernosa is enveloped in a fibro-elastic tunic, con- taining but feAV muscular elements, the tunica albuginea, v. fibrosa, from whichinnumerable bands and septa are given off internally, consisting of ordinary and elastic connective-tissue fibres, with a number of muscular elements. These bands, then, undergo repeated subdivision, and unite in every conceivable way; so producing a system of cavities communicat- ing with one another, like those of a sponge, and lined throughout with vascular cells or endothelium. Thus a peculiar venous receptical is formed for the blood. . The several cavernous bodies in man resemble each other, as a rule, in 37 568 MANUAL OF HISTOLOGY. structure. The description just given, however, refers more particularly to the corpp. cav. penis. These are separated from one another anteriorly by an imperfect partition. But, besides these, there is another cavernous body, the bulb of the urethra, quite distinct from them, and remarkable for having a thinner envelope, more delicate trabeculae, smaller receptacula, and a° larger proportion of elastic fibres. The interstices in the spongy tissue of the glans are even narrower still. The reservoirs just mentioned are constantly filled with blood, but become overcharged Avith the same at intervals, effecting that change in the male organ known as erection. In order to understand this phenomenon clearly, it will be necessary to review first of all the whole arrangement of vessels and circulation of the cavernous organs. In doing this we shall adhere to the description given in a very excellent work by Langer. The corpora cavernosa of the penis only receive a few inconsiderable twigs from the dorsal artery; they are chiefly supplied by the arterice ■profundus which run close to the septum. These are enclosed in a sheath connected with the cavernous cellular network, and give off gradually numerous anastomos- ing twigs to the cavernous sub- stance which run along within the trabeculae, and take a tor- tuous course in the quiescent state of the organ. The modes in which these vessels merge into the cavities of the venous spongy tissue are several. In the first place, they de- crease rapidly in diameter towards the surface of the corpora cavernosa, and more so still in the vicinity of the septum. Here we find true capillary networks of some- Avhat large-sized tubes at the point of transition. These con- stitute, as Langer expresses it, the "superficial cortical net- work," and (fig. 551, 1, a) com- municate with a "deeper sys- tem of wide venous canals" (b), "the deep cortical net- Avork." An immediate transition of fine arterial twigs (2, a) into these latter is also to be seen, however, which explains the rapid occur- rence of turgidity in the peripheral system of lacunae. Direct communication of terminal arterial twigs takes place also with the deeper venous receptacles of the interior, a remarkable funnel-shaped opening being evident at the point of transition (" Zapfen ") The trabeculae of the interior of the corpora cavernosa 'contain also Fig. 551.—From the peripheral portion of the corpus cavernosum penis, under low magnifying power. 1. a, network, known as the superficial; b, the deep. 2. Con- nection of arterial twigs (o) with the canals of tlie deeper cortical network (copied after Langer). ORGANS OF THE BODY. 569 wide-meshed capillary networks, which probably empty themselves like- Avise into the venous cavities of the part. Finally, the coats of the arteria profunda are supplied Avith a meshwork of capillary vessels. These gather themselves together to form venous twigs, also to be seen here, which empty themselves into a network of venous spaces surrounding the artery. The so-called arterice helicinae, brought into notice by /. Muller, and the subject of such frequent controversy, used to be supposed to terminate, after many contortions and tendril-like convolutions, partly with blind sac- cules in the cavernous spaces projecting into the latter. The appearances Avhich led to these conclusions were, however, artificial (Rouget, Langer), produced in part by imperfect injection, partly by the constriction caused by severed elastic trabeculae. The conveyance of the blood out of this system of lacunae is effected, in the first place, in the dorsal portion of the organ, by short venous passages, which spring from the deeper cortical netAvork, and empty them- selves into the dorsal vein of the penis (so-called venae emissaries). Again, by the venae emissariae inferiores, which come from the interior of the cavernous system, and make their exit near the urethral furroAv; lastly, by the vena? profunda? of the crura of the corpora cavernosa. In the spongy portion of the urethra we find a venous network inter- nally around the tube, consisting of long meshes connected with the venous lacunae. In the bulb alone do we encounter a direct entrance of arterial twigs into the lacunae: the transition in other localities takes place through the medium of capillary networks, as seen, for instance, in the mucous membrane of the urethra. In the spongy part of the glans, where the lacunar system is more or less replaced by genuine venous vessels, the connection between arteries and veins is everywhere effected through the medium of capillary inter- lacements (Langer). The lymphatics of the male urethra, connected with those of the bladder, are arranged in complicated networks, which, with longitudinally- arranged meshes, open directly into the lymphatic canals of the glans penis. The latter are numerous, but thinner than those of the urethra (Teichmann). They interlace in the uppermost layer of the skin in the form of wide passages, seen in greatest numbers in the glans, and less highly developed in the prepuce and other portions of the organ (Belajeff). The larger trunks derived from these course along the dorsum of the penis, and are received partly into the true pelvis, partly into the glands of the groin. The nerves of the penis are derived partly from the cerebro-spinal system (n. pudendus), partly from the sympathetic (plexus cavernosus). The latter are stated to supply the cavernous tissue alone; the first the skin, and mucosa besides. The skin of the glans is peculiarly rich in nerves. Many years ago Krause discovered terminal bulbs in this situa- tion, and since then genital nerve-corpuscles (p. 327) have been also observed. Tomsa mentions also a second and more simple mode of ter- mination of the nerves of the glans. Pacinian corpuscles also were found by -Schweigger-Seidel behind the glans, in the neighbourhood of the dorsal artery of the penis. In regard to the theory of erection of the penis. Lioelliker endeavoured, many years ago, to explain it as efiected by a relaxation of the muscular tissue of the corpora cavernosa under the influence of the nervous system. 570 MANUAL OF HISTOLOGY. This would naturally allow of the distension with blood of the small receptacles of the cavernous substance. Later Eckbart found in the dog fibres running from the plexus ischiadicus to the hypogastricus, which he showed to be the erection nerves. Loven found that during irritation of these a bright red stream of blood spurted from a small arterial tAvig suddenly on being opened; the pressure of the blood, at the same time, in the vessels of the penis continuing much less than in the carotid. Here, then, we have before us a relaxation of the walls of the smaller arteries brought about by stimulation of a nerve similar to that produced in the heart by irritation of the vagus. But, besides this, no doubt hindrance to the exit of the blood from the organ increases the erection. This is possibly brought about by the m. transversus perinaei (Henle) preventing the return through the roots of the penis. Also by the position of the venae profunda? in the corpora cavernosa, and the fact that the veins of the plexus pudendalis possess numerous projections of smooth muscles. B. Organs of the Animal Group. 6. Bony Apparatus. §288. Although we have already referred at some length, in the second part of our Avork, to the bony apparatus or osseous system in dealing with the tissues of Avhich bones are composed, there still remain some comple- mentary considerations which must occupy us for a few moments. These are, in the first place, the mode of connection of the various portions of the skeleton with one another; secondly, the vessels and nerves of bone; and thirdly, the substance with which the cavities of the latter filled up. The Avays in Avhich bones are joined together are, as is well known, very various. While in the embryo the connecting masses are, in all proba- bility, almost universally solid, but a small number of them remains so at a later period. In such instances they are knoAvn to anatomists as examples of synarthrosis, a mode of connection represented in sutures and symphyses. In other rudimentary masses of this kind a process of liqui- faction in the interior gives rise to the formation of cavities, while the peripheral cells of the mass are transformed into the tissue of a capsule, with its epithelial cells, &c. This mode of connection is designated as diarthrosis, or jointed union. If, as is often the case with symphyses, the process of liquifaction should cease at an early period, we have what has been called half joints (Luschka). The latter are usually somewhat ill-defined, and are variable in nature : no synovial capsule is to be reeoc- nised in their interior. In regard now to the several media of articulation between bones, the suture is united by what is incorrectly named suture-cartilage, which is nothing less than a fine band of whitish fibrous connective-tissue. Sym- physis is effected by hyaline, or fibrous cartilage and connective-tissue. Here the ends of the bones are clothed with a layer of hyaline substance which, covered externally by connective-tissue, completes the union * or this cartilage passes gradually, more and more, into a fibrous mass, Avhich may at certain points give way to pure connective-tissue. We have already referred to this texture, in speaking of fibrous cartilage, in § 109, where the intervertebral disks were fully described. The symphysis pubis and sacroiliaea are half joints, as also almost invariably the points of union of ORGANS OF THE BODY. 571 the costal cartilages with the sternum from the second to the seventh rib We not unfrequently meet in the symphyses Avith a layer of calcified car- tilaginous tissue in the vicinity of the bone. The further consideration of these parts must be left to works on descriptive anatomy. As regards the joints, we have already considered their cartilages (§ 107), and in § 109 their labra cartilaginea, sometimes present. Under the cartilaginous coverings of bones forming joints Ave very generally find a layer of peculiar undeveloped osseous tissue. It is, on an average, 0*27 mm. in thickness (Koelliker), and consists of a yellowish and usually fibrous solid mass, which presents, however, neither Haversian canals nor bone corpuscles. Instead of these, we observe iu thin sections cartilage capsules filled with air. A description of the tissue of the synovial capsules will be found in § 135. The latter are very vascular, and are richly supplied, apparently, with lymphatics (Teichmann). They are strengthened externally by the addition of strong fibrous tissue. Their epithelial lining has been already discussed, as far as it occurs, in § 88, and the synovia itself in § 97. For a description of the inter-articular cartilages—those disks of connective- tissue cartilage attached laterally to synovial capsules, and interposed between the heads of bones forming joints—compare § 109. The liga- ments of joints consist of connective or fibrous tissue (§ 135). From the frequent deposit of fat-cells in the connective-tissue envelop- ing synovial capsules, it is often found, as already alluded to in § 122, that collections of the former are protruded into the cavity ofthe joint in the form of duplicatures. These are most usually met with in the knee and hip joints, and are known there as the glands of Havers. The appear- ance, however, of very vascular fringed folds of synovial tissue is of far more frequent occurrence, and encountered in almost all joints. These are usually destitute of fat-cells, and present occasionally a few cartilage elements intermixed Avith those of the connective-tissue. They have been given the name of plica? vaseulosae (1), and are represented also in the half joints, according to Luschka, although devoid of vessels in those situations. Remarks (1).—The structures in question are frequently covered with smaller pro- cesses, leaf-shaped or membraneous, and sometimes of the strangest shapes. From these the loose cartilages found at times in the interior of joints are derived, though not exclusively. They consist of more or less calcified cartilage, and occur most frequently in the knee. Compare Virchow, " Die krankhaften Geschwiilste," Bd. i. 5, 449. §289. As regards the blood-vessels of bone, we have to bear in mind, in the first place, that the periosteum (§ 135) is very vascular. . It is supplied by a number of large vessels, which pierce it, however, for the most part, only on their Avay to supply the osseous tissue beneath. It is possessed, further, of finer-vessels proper to itself, Avhich are arranged'in rather com- plex capillary networks. In order the better to comprehend the arrangement of the vessels of osseous tissue, let us first take one of the tubular bones as an example. As we have seen above, numerous vessels from the periosteum are given off to the openings of the Haversian canals (§ 140), and are there arranged in a long-meshed network of tubes of considerable size, which often assume characters different from those of true capillaries, and belonging rather to the smaller veins and arteries. Beside this, we ahvays meet with a large single or double canal in the diaphysis of such a bone, the foramen nutri- 572 MANUAL OF HISTOLOGY. tium, into which an arterial twig is sent Avhich makes its way eventually into the central medullary canal as the arteria nutritia. The latter then divides into an ascending and descending branch, which again break up into a capillary network, including the fat-cells of the medulla in its loops (see below), and giving off a' series of vessels which enter the internal opening of the Haversian canals to anastomose with those coming from the periosteum. In the epiphyses, also, the supply of blood is partly from without, through small vessels derived from the periosteum, or larger tAvigs entering through the more numerous nutritious foramina of these portions ; and partly from within, through close connection with the vessels of the medullary canals of the diaphysis. These vessels, then, are situated, in the first place, within the Haversian canals, and again distri- buted through the medullary cavities. The course of the veins is analogous to that of the arteries. One set of venous vessels convey the blood out of the part through the larger and smaller nutrient canals; another set of branches return to the periosteum by the peripheral openings of the smaller medullary canals. Turning now to the other kinds of bones—to the short and tabular, namely,—we find that they present the same arrangement of vascular supply as the epiphyses, Avith the exception of the flat bones of the head. Through the many openings, namely, on their surfaces, small arteries and veins make their entrance and exit: their terminal branches are found, however, more in the medullary cavities than the scanty Haversian canals. The flat bones of the cranium, on the other hand, are supplied by numerous fine arterial twigs, which enter through holes in the two vitreous plates, and break up in the cavities of the diploe' into capillaries interlacing amongst themselves. The veins, hoAvever, present themselves, as was discovered by Breschet, in quickly-branching wide bony canals, in the form of very thin-walled tubes traversing the diploe in various direc- tions, and emptying themselves partly into the external veins of the head, and partly into those of the dura mater. The cartilage covering the ends of bones is quite destitute of vessels. The existence of lymphatics in osseous substance has not been demon- strated to a certainty. The nerves with which bones are supplied present the same arrange- ment as the blood-vessels. The periosteum is very richly supplied wfth them ; but the greater proportion simply pierce this membrane to reach the osseous tissue beneath,—so that, in fact, but a small number properly belong to it itself. In this respect, however, the periosteum varies greatly, according to locality : in some spots it appears to be quite without nerves' while in others it is richly supplied. The nerves consist of broad and medium-sized fibres which split up before their termination. One set of nerves enter the bone with the blood-vessels which pass through the periosteum, by means of the Haversian canals : these are very fine. Other stronger twigs find their way into the interior through the foramina nutritia. From thence they are distributed to the larger medul- lary cavities. Their ultimate termination is still a matter of doubt! Many of the short and flat bones are, according to Koelliker, very highly innervated Most of the nerves are derived from the cerebro-spinal system. The capsules of the joints are also very rich in nervous supply while the ligaments are but scantily furnished with sentient elements. ' The cavities of the bones are filled up with a substance known as the marroio. This presents itself under two forms, with intermediate vario- ORGANS OF THE BODY. 573 t es. In the long bones it is met with as a yellow mass, found under the microscope to be made up of scanty bundles of connective-tissue interspersed with fat-cells (fig. 552, d, e). Chemical analysis shows it to be composed of neutral fats to the amount of 96 per cent., according to Berzelius (comp. §§ 122 and 147). * In the epiphyses, on the contrary, and in flat and short bones, the medulla is a reddish or red mass of soft consistence, made up usually of bundles of connective-tissue similar to those of the last variety (but in smaller quantity), Avith an ever- decreasing number of fat-cells containing, on the other hand, numerous small contractile lymphoid elements, with granular contents and distinct nuclei. These latter, 0*0090-0*0113 mm. in diameter, are identical with the cells figuring in plate 552, b, from the medulla of an infant. Like them, they were formerly supposed to be descendants of the cartilage medullarv cells (§ 147). On the surface also of the yellow variety of medulla, cells of this kind are to be met with here and there. An interesting point, in regard to these lymphoid cells of the medulla of bones, has recently been noticed by Neuman and Bizzozero in the osseous tissues of man and other mammalia. This is the transfor- mation of the former into red blood cor- puscles, reminding us of the formation of embryonic blood. The possibility of im- migration of these into the vessels of the medulla is suggested. Another kind of element is also to be found in the medulla of bones, and, more- over, at all periods of life, namely, large isolated membraneless multi- nuclear cells, knoAvn as myeloplaxes (p. 258). According to Berzelius, red medullary substance from the diploe contains 75*5 per cent, of Avater, traces 24*5 of solid constituents, protein compounds, and salts, but merely of fatty matters. 7. Muscular Apparatus. § 290. The structures Ave are uoav about to consider briefly have been already described in the second portion of our Avork in dealing Avith muscular tissue (§§ 162-173). The structure ofthe tendons formed the subject of § 134, belonging as they do to the connective-tissues, among Avhich the fascitis also are included. In § 109 the fact Avas also mentioned, that at those points Avhere tendons are inserted into bone, deposits of cartilage cells are not unfrequently met with between the bundles of fibres, of which the structure is chiefly composed, thus giving rise to a kind of fibro-cartilage. That the same cartilaginous tissue may be developed iu the interior of tendons was also remarked in the same place. Here, then we have the source of sesamoid cartilages, whose place again may be taken by analogous osseous formations knoAvn as sesamoid bones. The blood-vessels of the tendons can be only found with great difficulty nay further, small sinews are entirely destitute of them, and are supplied entirely by a wide-meshed network contained in the connective-tissue in Fig. 552.—Medullary cells of cartilage, o, from the humerus of a human foetus at five months; b, from the same hone of an infant shortly after birth; c, stellate and fusiform cells from the first; d, formation of the fat-cells of the marrow; e, a cell filled with oil 574 MANUAL OF HISTOLOGY. Avhich they are enveloped. Large tendons contain in their superficial layers isolated vessels; while those of greatest magnitude are supplied Avith blood-vessels as far as their internal laminae, while that portion farthest from the surface remains non-vascular. The mucous or synovial sheaths of'the tendons, vaginae synoviales have been already described in speaking of the latter. The synovial sheaths of muscles have also a similar structure, as likewise the bursa-, mucosae. Most of these are, however, by no means shut serous sacs, as was formerly sup- posed : this is only in some measure the case here and there. The same may be said of the epithelial lining of simple flattened cells (§ 87): it is only met Avith in portions of the capsules, in the Avails of which, further, a sprinkling of cartilage cells may be met with. The contents of all these cavities have been already dealt with in considering the synovia (p. 155). In § 168 the blood-vessels of the muscles are dealt with, and the nerves of the latter in § 182, with the nervous system generally. The lymphatics, as far as Ave may judge from the scanty observations which have up to the present been made upon the subject, present themselves in muscular tissue in but small number (Teichmann). They were found, hoAvever, by Tomsa in the interstitial connective-tissue betAveen the fibres of these organs in the dog : another superficial set, also, is described by His. 8. Nervous Apparatus. §291. The greater part of the nervous system has already come under con- sideration in an earlier portion of our work (§ 174-192): there still remain, however, the brain and signal cord. The medulla spinalis (1), a cylindrical nervous cord, con- sists of an internal grey or greyish-red, and an external white substance. The first, prolonged throughout the whole length of the cord, has, on transverse section of the latter (fig. 553), the shape generally of the letter H; that is, it may be said to con- sist of a middle portion, two anterior (d) and tAvo posterior cornua. The latter, further, are enclosed within another clear gelatinous layer, known as the substantia gelatinosa of Rolando (/). In the middle of the grey substance a deli- cate central canal (c) is ob- served, the only trace left of the rudimentary groove Avhich gradually closed in to form the foetal spinal cord. It is lined within bv cdiated epithelial cells (§ 93). J The circumferential white substance presents deep indentations both Fig. 553.—Transverse section of the spinal cord of a calf (after Ecker). a, anterior, 6, posterior median fissure; c, central canal; d, anterior, e, posterior cornua; /, sub- stantia gelatinosa of Rolando; g, anterior column with motor roots; h, lateral column with connective-tissue partitions; i, posterior column with sensitive roots; *, anterior, and /, posterior transverse commissure. ORGANS OF THE BODY. 575 before and behind, the anterior (a) and posterior medium fissures (b), so that its two halves are only connected at the bottom of the anterior fissure by a white band (k), the white commissure or commisura anterior. The isthmus however, contains besides a band of grey substance, known as the posterior commissure (1). The white matter of the cord may be con- sidered as consisting of three imperfectly defined symmetrical longitudinal bands,—the anterior (g), lateral (h), and posterior {i) columns. In the cervical portion of the spinal marrow the latter most internal and posterior portion constitutes what is known as the band of Goll, to which Ave will again refer in speaking of the medulla oblongata. At the junction of lateral and anterior columns the motor roots of the spinal nerves penetrate as far as the anterior cornu; while the entrance of the posterior sensory roots takes place in a similar manner at the point of union of the middle and hinder columns. Looking at it from a histological point of view, the Avhole spinal marrow may be said to be supported interstitially by a lowly-organised vascular connective-tissue, and to be composed of nervous fibres and ganglion cells imbedded in this framework. In the white substance, hoAvever, we find fibrous nerve-elements alone, but in the grey, besides these, ganglion cells. There are, hoAvever, so many difficulties still connected Avith the investigation of the more minute arrangement aud combination of these nerve-elements, that, with the brain, the spinal cord may be said to be one of the most obscure and unsatisfactory fields of modern histological research. One of the obstacles to advance in this direction is, that we are unable here to draAv any sharp line of distinction betweeii nervous and connective-tissue constituents (see § 119). One school of histologists belieAre that connective-tissue constitutes a very large portion of the sub- stance of the spinal cord, Avhile quite the opposite vieAv is held by another party. Remarks.—(1.) Literature is very rich in treatises on the structure of the spinal cord. Besides numerous Continental essays by Stilling and JVallach, Schroder van der Kolk, Koelliker, Reissner, Deiters, Gerlach, may he mentioned those of Lockhard, Clarke, Philos. Transact. 1851, p. ii. p. 607, and p. iii. p. 347; and Scale's Archiv. of Medic. 1858, p. iii. p. 200. Further, in the Proceed, of Roy. Soc. vol. viii. No. 27; and Philos. Trans. 1858, p. i. p. 231, and 1859, p. i. p. 437. /. Dean's Microscopical Anatomy of Lumbar Enlargement of the Spinal Cord, Cambridge {U.S.) 1861. W. Hendry in Micros. Journ. 1863, p. 41. § 292. We shall now consider the neuroglia or connective-tissue sustentacular substance of the spinal cord, whose chief peculiarities have been already touched on in a former section (§119). In it we have a framework, as it were, for the medulla, in contact with the pia mater externally, and continuous throughout the Avhole cord, though of by no means of the same structure in the different divisions of the latter. We find it in its simplest form surrounding the central canal as a ring merging imperceptibly at its periphery into the grey matter. To this several names have been given, such as " central ependymal thread," " grey central nucleus," " gelatinous central substance." It presents itself here as a soft substance of homogeneous, streaky, or even at certain points finely fibrous appearance. Filiform processes from the epithelial cells of the axis canal project into it, as also connective-tissue ramifications of the pia mater from both fissures of the cord. Cellular elements may also be 576 MANUAL OF HISTOLOGY. Fig. 554. — Sustentacular connective-tissue from the posterior column of the human spinal cord, showing the nerve- fibres in transverse sec- tion. recognised as entering into the composition of this ependymal tissue. They appear to have been formerly incorrectly described as nerve-cells, of which, as -well as of nerve-fibres, this tissue is entirely destitute. The substantia gelatinosa of Rolando, mentioned in the preceding section, presents also purely connective-tissue characters. It is remarkable for its richness in cellular elements. Some very few nervous constituents may be observed in it in the form of scattered fibres. But the sustentacular substance in the grey matter of the cord is far less pure: it is mixed up with nerve-fibres, ganglion cells, with their various processes, and blood-vessels. It forms here a finely porous spongy tissue, referred to already at § 119, of the most delicate texture, with numerous free nuclei or (if the latter still retain a thin layer of protoplasm) Avith the equivalents of small cells. The connective-tissue framework of the white substance, hoAvever, attains a greater degree of massiveness. In trans- verse section (fig. 554) it appears homogeneous or streaky, dotted at its nodal points with nuclei, and forming so a lace-work as it were, in whose meshes the transverse sections of the nerve tubes are to be seen ; while in longitudinal cuts a more or less regu- larly tubulated appearance is presented by the slice, Avhich may also show oblong deficiencies of substance. Larger collections of connective substance some- times form radiating partitions around groups of nerve-fibres, giving by their numerous intercommuni- cations a net-like appearance to the Avhole (fig. 553, h). Towards the periphery of the cord the sustentacular substance is again much more highly organised, and is free from nerve-fibres (Bidder, and Kupffer, Clarke, Koelliker, Frommann). Lastly, the pia mater covers the* surface of this grey cortical layer. Turning now to the blood-vessels of the cord (fig. 555), it may be usually observed in transverse sections that from the branches of the art. med. spin, anter. two twigs are given off in the anterior fissure, which pass into the substance of the spinal marrow, and that a third twig, cor- responding to them, lies in the poste- rior fissure (b, c). Other finer arterial tubes are conducted into the white substance (/, g, h) by the radiating bands of connective-tissue of the pia mater. It is from these principally that the capillary interlacements of the white matter are supplied, which are here particularly large meshed and composed of very delicate tubes.' The capillary network of the grey It is chiea, derived from the arteries S uSta.»"jS S^"* *'' nected at all point, of its periphery with the »*Jl"S^ Fig 555.—Transverse section in the dorsal region of the medulla spinalis of the cat. a Cen- tral canal; b, anterior, c, posterior fissure- a, anterior cornu; e, posterior cornu; / a h white columns, with their wide-meshed\^»1 lary networks. ieir wide-meshed capil- ORGANS OF THE BODY. 577 Of the veins, two are specially striking in the neighbourhood of the central canal (Clarke, Lenhossek). Some years ago the arrangement of the capillary network of the cord was very minutely studied by Goll. The widest meshes were found by him in the anterior columns, the finest in the lateral, while those of the posterior columns lay between the two. But the densest capillary inter- lacements of all are to be met with in the grey matter in those situations where many ganglion cells are collected together. Finally, the restiform bodies are remarkable for having meshes of capillaries as small as those of the grey substance. It has been already mentioned (§ 207) that throughout the Avhole spinal cord and brain, all the blood-vessels, including arteries, veins, and capd- laries, are invested with a loose sheath of connective-tissue. A watery fluid found within the latter has been regarded by some as lymph. The existence, however, of this system of perivascular canals of His is not yet firmly established, and has lately been the subject of very earnest controversy. § 293. Having now discussed the connective-tissue groundwork of the cord, let us turn to its nervous elements. The white substance, as has been already remarked, consists entirely of fibres. These present all the characters of central structures (fig. 556, /, g, li), i.e., they are not supplied with the same primitive sheath as the peripheral tubes, so that in many cases Ave are only able to obtain them in broken fragments. In the finer specimens further there seems to be a tendency to varicosity (§ 176), and we may easily recognise their axis cylinder. Their diameter may be roughly estimated at from 0*0029 to 00090 mm., show- ing, that besides very fine elements, broader ones also exist. * It appears beyond doubt, further, that these central fibres divide, although we are confined to conjecture at present as to the frequency of the occurrence. Passing on to the arrangement of the nerve fibres in the Avhite columns of the cord (fig. 557), we have to discriminate between bundles which hold a longitu- dinal, a horizontal, and an obliqUe course. The greater proportion of fibres belong to the first of these classes (I, m, n), and are often unmixed with bundles having any other direction. Their course in the peripheral portions of the cord is regularly parallel, while in the vicinity of the grey matter they generally may be observed to interlace, and to be collected in small fasciculi. Further, and in this Ave have probably an important physiological fact, certain regular differences in the diameter of those nerve fibres of the white columns are manifest. In the first place, the more internal, lying close to the grey matter, Fijr. 556.—Different kinds of nerve fibre?, /, g, h, central; therfibre g, as axis cylin- der, is continuous above, with the pio- cess of a ganglion cell. 578 MANUAL OF HISTOLOGY. n are remarkable for their small diameter, as compared with their fellows situated more externally. One spot in particular presents very fine fibres, namely, close to the inner angle of the lateral column, Avhere the anterior and posterior cornua meet. Very characteristic differences in diameter are also apparent, if we com- pare the chief masses of fibres of the various columns. The anterior (I) possess the broadest, and consist principally of such. Those bundles of the lateral column in the vicinity of the grey matter are made up of very fine elements. Further out towards the periphery a stronger series is to be found occurring with great regularity (m), and in- termixed more externally still with small fasciculi of finer fibrillae. The fibres of the pos- terior column, compared with those of the anterior, are dis- tinctly smaller in diameter. But in the bands of Goll we meet writh the most delicate filaments of all disposed Avith the utmost regularity. Let us noAv turn to the transverse and oblique sys- tems of fibres coursing through the Avhite columns. These, Avithout counting the elements of the two com- missures, consist of the root- bundles of the spinal nerves (i, k) emerging from the grey cornua, and intersecting the longitudinal bands of fibres of the white substance. But it is only the posterior sys- tems of fasciculi that run really horizontally, the motor root-bundles take an oblique course Lhe anterior or motor roots pass through the white substance in several fasciculi, and with a tolerably straight course, separating the anterior from the lateral columns. In this ivay they arrive at the anterior cornu still in the form of broad fibres, and then break up into delicate elements which radiate in all directions, and in various planes, forming at the same time numerous loops. Many take their course along the surface of the cornu inwards, man arch towards the anterior longitudinal fissure. Others again, are directed outwards towards the boundary of the lateral column' turning round again and running inwards. Other bundles, again, may be followed directly backwards as far as the base of the posterior cornu In order the better to understand their further destiny, let us accom- pany these nervous fasciculi into the anterior cornu, and in the verv first place inquire into the complicated structure of the grey matter In the delicate spongy mass, of which its sustentacular tissue is com- posed we see, in the first place, an inextricable maze of fine and extrenieTy delicate nerve filaments. Then, in the anterior cornu large multipolar Fig. 557.—Transverse section through the under half of the human cord (after Deiters). a, central canal; b, anterior- c, posterior fissure; a\ anterior cornu, with large ganglion cells;_«, posterior cornu with smaller; /, anterior white commissure; g, sustentacular substance around the cen- tral canal; h, posterior grey commissure; t, bundles of the anterior, and k, of the posterior spinal nerve roots- l, anterior; m, lateral; n, posterior column. ORGANS OF THE BODY. 579 ganglion cells (d) are ODserved, imbedded in the sustentacular substance of the part. These are not unfrequently tinged with brown pigment, and vary considerably both in shape and in the number of their pro- cesses. They are specially numerous at the apex of the anterior cornu, Avhere they usually form several dense clusters as it were. Here they are separated from one another by interposed broad nerve fibres. Other scattered multipolar cells, however, are met Avith singly, and especially towards the surface of the grey substance. In the most internal portions of the cord also, near the axis, as also at the base of the posterior cornu, we find them still presenting precisely the same essential characteristics, though decreased in size. The numerous processes of these ganglion corpuscles spread them- selves out in all directions, and, as a rule, are soon lost to view by dipping into other planes. As observed by Deiters, Avhose statements we here follow in regard to many points, these processes may penetrate into the radiating septa of connective-tissue running through the white substance; others, also, may be regularly looped around bundles of nerve fibres in certain cases (Clarke, Deiters). These groups of multipolar ganglion cells have been very commonly described as connected with one another by means of some of their rami- fications, and great stress has been laid upon the importance of the latter as commissures. It cannot be denied, however, that a deplorable misuse has been made of this supposed existence of connecting fibres (fig. 305, p. 314). and it is only extremely rarely that a perfectly unmistakable vieAv can be obtained of them. Thus, in the works of many authors it is openly con- fessed that, with all their efforts, they Avere never successful in obtaining a sight of anything of the kind (Goll, Koelliker). Others even deny the existence of such commissures altogether (Deiters). Others, again, are able to state that they have observed them, but in rare instances (Reissner). Our own experience coincides with that of the latter. Even Dean, a very sound observer, who is, notwithstanding, somewhat too profuse Avith such commissural processes, only speaks of them as exceptions. A second widely received axiom in the anatomy of the spinal cord, is that other processes of the ganglion cells become the axis cylinders of the nerve fibres of the anterior roots. This also is asserted on many sides with great certainty to be quite easy to see, Avhereas it is a matter of the greatest difficulty in reality to obtain even one clear instance of it, some observers honestly confessing their ill fortune in this respect (Goll). As a rule, under favourable conditions, one such process may perhaps be observed uniting with one of the motor root-bundles (Clarke, Dean, Ger- lach, Frey). Deiters, a recent and very thorough investigator, has added much to our stock of knowledge on this very abstruse subject of the relations of the central "ganglion cells. We have already referred to his important and repeatedly confirmed discovery (§ 179), that the ramifications ofthe ganglionic bodies are of two kinds (fig. 558). In the first place, wide branching processes of protoplasm (6) present themselves, and then for every cell another smooth undivided one (a), the axis cylinder process. This observer, nevertheless, states that only in exceptional cases was he able to follow up the latter for any distance in a section of the spinal cord As may be seen in our plate, there also spring (usually at right angles) from the broad protoplasm processes of the cell, a number of other very delicate fibrillse. These Deiters regards as a system of secondary axis 580 MANUAL OF HISTOLOGY. cylinders for the most delicate nerve fibres, as we have already briefly stated (p. 315). But probably the end filaments of all these tree-like processes eventually acquire the same constitution. The fact that both species of processes, namely, the branched proto- plasm and the axis cylinder, may be observed to be marked with fine lines, indicating fibrillation (Schultze), has been already alluded to (p. 316, fig. 308). The cells also situated close to the central canal, and those as far back Fig. 558.—Multipolar ganglion cells from the anterior cornn ofthe SDinal cord of the ox a, axis cylinder process; 6, finest filaments springing from the ramifying protoplasm processes. "*e»>b as the base of the posterior cornu, present the same remarkable structure recognised by Deiters. The destiny of these " protoplasm processes " however, is by no means settled as yet. According to Gerlach they first break up into a delicate, dense network of nervous nature, from which the nerve fibres then spring, or (if we prefer the converse) into which they sink after previous ramification. Going further backwards still, regularly into the posterior' cornu (fig. ORGANS OF THE BODY. 581 55 <, I), we encounter smaUer cells, in many cases fusiform and of delicate consistence. In them also one process becomes an ordinary, though thin axis cylinder, beside which may be seen again ramifying protoplasm pro- cesses with lateral derivation of the finer axis cylinders of the second order. In size and shape these cells also vary considerably, larger examples resembling in a great measure those of the anterior cornu. lhese corpuscles of the posterior cornu have been set down as the source of the fibres ofthe sensitive roots, and been designated as sensory elements, although at present we are possessed of no really complete proof of the correctness of this view: Gerlach reckons them, moreover, among the motor ganglion corpuscles. At the base of the posterior cornu, internally, almost throughout the whole length of the cord, other small groups of cells are to be seen (the pillars of Clarke, or nuclei of Stilling, according to Koelliker). The elements, collected here, are of medium size, round, and ramifying. Very little is as yet known about them. According to Gerlach, further, they are not possessed of an axis cylinder process. Their ramifications merely sink into the dense neural network of the grey substance. The proper ganglion cells of the posterior cornu possess, as a rule, in the opinion of the last-named observer, processes only, which merge into that nervous reticulum just spoken of. From the latter, then, the sensory fibres of the posterior roots arise. From all this it would appear that the mode of origin of the motor and sensory nerve fibres is entirely different. The delicate neural net-work alluded to is only observed to be absent in the immediate neighbourhood of the axial canal, and in the substantia gelatinosa of Roland. It may be easily distinguished from the elastic reticulum of the neuroglia by certain reactions according to Gerlach. §294. Turning noAv to the posterior roots of the cord (k), we find far greater complication than among the motor bundles of the spinal nerves. Our knoAvledge, therefore, of the nature of their arrangement is necessarily more scanty than of the latter. The remarkable diminution, besides, in diameter which the sensitive nerve fibres undergo on entering the grey matter, renders the tracing of them very difficult. It is stated by some (Koelliker) that the external portion of the pos- terior root-bundles passes directly through the posterior column into the grey substance. Another, and moreover larger part is said, on the other hand, to pursue a rather devious curving course through the hinder column, bending round subsequently in order to pierce from the side the convex border of the posterior cornu, which is turned towards the middle line. From this the fasciculi advance toAvards the anterior cornu, passing partly into the anterior commissure, and partly in among the posterior group of motor ganglion cells; or, again, penetrating at times as far as the anterior portion of the lateral column, Avhere they are lost. The first-men- tioned bundles are said to pass forwards, partly as separate longitudinal fasci- culi, tending at the same time with radiation towards the centre, in order to arrive at the pillars of Clarke,&s they are called, without becoming connected with cells. Some of them reach the anterior cornua and commissure. Commenting on these statements, Deiters showed later that it is always the greater part of the posterior root which takes this curved course through the posterior column, and enters the cornu from it. Here 582 MANUAL OF HISTOLOGY. we see the substantia gelatinosa of Roland traversed in its whole circum- ference by separate fasciculi of very delicate fibres, Avhich advance later into the base of the posterior cornu in part, or, taking another direction, enter the pillars of Clarke. Other bands of fibres may be observed to pass forwards through the latter, disappearing eventually in the grey matter beyond. Others, again, are said to enter the posterior commis- sure, and many, probably, the grey matter of the anterior. So far, then, it appears at least possible, that all the fibres of the posterior root penetrate into the grey matter. And in that they here probably pass between sensory ganglion corpuscles, we might expect a (direct or indirect) connection with the latter. An immediate turning in of a portion of the posterior root into the posterior column in order to pursue a course towards the brain ("sensory fibres" of Schroder van der Kolk) appears for many reasons very unlikely. According to Deiters the three Avhite columns—mainly composed of the conducting portions of the cord—may be regarded as springing from the grey matter, and the system of the ganglion cells as interpolated between them and the roots of the spinal nerves. Accepting this as correct, the ganglionic cell system Avould appear to possess the significance of a provisional central point, from which the neural tract, altered in direction, and in all likelihood simplified, takes its course onAvard to the cerebrum. It must, hoAvever, be designated as a mere point of histological dogma if all the fibres of the roots be stated to have such a connection with ganglionic corpuscles. Whether the very fine protoplasm processes of the latter, discovered by Deiters, are commis- sures between the ganglionic cells; Avhether after further isolation, and increase in breadth, they become the axis cylinders of the nerves of the white columns; whether for the formation of one of the latter axial structures, several of these very delicate fibrilke first combine, or whether, as Gerlach maintains, the latter form a netAvork of filaments of the most extreme tenuity,—are all questions to which science is unable at present to give satisfactory answers. The same want.of facts is felt in regard to the existence of a connection between motor and sensitive cells. It is generally supposed that the anterior columns serve as conductors be- tAveen the motor nerves and the brain, and the posterior between the latter and the sensory nerves, while the lateral cords partake of the nature of both. We shall now conclude this extremely unsatisfactory description with a brief mention of the two transverse commissures of the spinal cord. If we examine the most anterior of these bands (/) closely, we shall soon convince ourselves that a number of genuine nerve fibres exist in it, enclosed in sustentacular connective-tissue, and intersecting each other at various angles. In the medulla spinalis of the calf and ox, in which the relations of parts may be very clearly seen (Deiters), the transverse inter- secting bundles advance even into the Avhite substance of the anterior column. They arise in the grey matter on one side, and after descending and again ascending to a certain extent in their course, arrive in the fibrous substance of the anterior column on the opposite side. No con- nection Avith ganglion cells can be demonstrated with certainty. Many have argued from this a total decussation of the motor nervous tracts in the spinal cord; but, perhaps, without sufficient grounds. At certain points, also, in the grey portion of the anterior commissure, fine nerve fibres may be observed to pass across from one side of the cord to the other. In the posterior commissure (h), likeAvise, we have a connective-tissue ORGANS OF THE BODY. 583 framework, intersected by a number of nervous bands, of great fineness however. Ihe latter, it is stated by some, may be seen to be connected in part with the lateral columns, in part with the posterior or sensitive nerve roots, and in part to be lost in the grey substance at the junction of the anterior and posterior cornua. §295. We come now to the consideration of the medulla oblongata, whose complicated structure involves us in far greater difficulty even than that of the medulla spinalis. The earlier investigations of Stilling, Schroder van der Kolk, Koelliker, Lenhossek, Clarke, and Dean, all led to different conclusions. But considerable light has since been throAvn upon the subject by Deiter's observations, and later still by Meinert's studies. In order to recall to the mind of the reader the rough anatomy of the medulla oblongata, it may be remarked, in the first place, that this con- necting link between cord and cerebrum has one of its numerous pecu- liarities impressed upon it through the central canal. The latter, namely, opens out gradually into the sinus rhomboideus or calamus scriptorius, and is continued as the fourth ventricle upwards. From this alone it is evident that a most essential change in position of the various columns and collec- tions of grey substance must take place ; parts situated close to the central canal, at a lower point on the cord, must now be displaced laterally. But Avhile this spreading out takes place on the dorsal aspect of the cord, the anterior fissure begins to close in to form the raphe (fig. 559, r). Besides these changes Ave now remark a num- ber of different parts visibly distinct from one another even externally, and known by special names. At either side of the anterior median line the pyramids, with their remarkable decus- sation, are first seen. Then external to them, and bounded on both edges by ascending fibres, the (inferior) oli- vary bodies appear. Ad- joining these we next observe the so-called la- teral columns (funiculi laterales), and behind them (later on quite ex- ternal) the corpus resti- forme of each side, or funiculus cuneatus, with Fiir 659—Transverse section of the medulla oblongata (after Dean). R, raphe; 0, olivary bodies; H, hypoglossus; and V vagus; r, posterior cornu; a, arched fibres; 12, hypoglossus and 10, vagus nerves. the /. gracilis in the cervical portion of the cord—a prolongation of the band of Goll. , . , , ,, The medulla oblongata is covered above and anteriorly by the pons Varolii, and at either side may be seen to be connected with the cerebellum bv means of thick cords known as the crura cerebelli. J 38 These may be 584 MANUAL OF HISTOLOGY. divided into two portions, namely, the crura cerebelli ad medullam oblonga- tum and adpontem. The pedunculi cerebrii connect it with the cerebrum. Finally, numerous nervous trunks spring from the medulla oblongata. Turning now from this mere outline sketch to the structure as seen with low magnifying poAvers, the full peculiarity of the medulla oblongata soon strikes us. The cornua of the central grey mass, as found in the medulla spinalis, become rapidly changed here, the alteration of shape commencing at the point of junction of anterior and posterior cornu, and spreading from thence further and further. Instead, namely, of the continuous grey sub- stance of another part of the cord, the cineritious matter here assumes the appearance of a series of bands or network, through which nerve fibres take their course (formatio reticularis). This metamorphosis then gradually extends, affecting eventually the white columns also almost throughout the whole medulla oblongata. Here and there, however, masses of grey matter still remain undis- turbed, Avhich are known as the nuclei of the medulla oblongata; these give rise to further peculiarities. Such nuclei are of two kinds. From one set of them the nerves springing from the medulla oblongata seem to take their rise primarily : these are the nerve nuclei of Stilling. A large 'number of them may be recognised, as we shall see later on. They have nothing absolutely new in them as compared with the spinal cord, and are equivalent to the sources of origin of the spinal nerves. But in addition to these, Ave meet with collections of ganglionic matter presenting other characters. These have nothing to do with the origin of peripheral nervous tracts ; they seem rather to be the points at whicli the fibres and cords of the medulla oblongata end provisionally, previous to their becoming changed both as to number of fibres and direction, and making their way into the brain. Among these specific nuclei, as Ave shall call them for shortness' sake, may be numbered, in the first place, the inferior olives (olivary bodies, in a word), with the accessory olives; then the superior olives, formerly erroneously held to be an upper nucleus for the trigeminus by Stilling, and a grey nucleus of considerable size imbedded in the lateral column, and named by Schultze the nucleus of Deiters; then, again, the pyramid nuclei and so-called ganglia post-pyramidalia of Clarke, situated in the posterior columns ; and further, the special grey masses of the pons Varolii. Takino- a still wider view with Deiters, we may include here the corpus dentatum cerebelli, the grey collections in the interior of the crura cerebelli, as well as those constituting the greater part of the corpora quadrigemina The bundles of white fibres, then, .ascending from the medulla spinalis although they may be found again in the medulla oblongata, preserve no longer their original uniformity of direction, but pursue, in many cases a totally different course. ' Besides the latter fasciculi, there appears in the medulla oblongata another very peculiar and complicated system of nerve tubes —that of°the transverse, arched, and circular fibres (a, a). This was kamed many years ago, the zonal by Arnold. In the raphe a very complex